With a few obvious exceptions, my answer to "can Christians watch..." is generally "yes", though there are a variety of things to consider. Nevertheless, unless there is specific sin involved, such as porn (which cannot be made, nor enjoyed, without sin), I think the only people qualified to answer whether or not you can watch a certain movie are yourself, maybe your parents if you're younger, and, of course, the Holy Spirit. As Christians, we don't get to run around telling our brethren what movies they can and can't enjoy.
Sadly, many in the Church disagree. Certain movies, they claim, can never be enjoyed by Christians. It is a grievous sin to watch these movies. A popular target for these kinds of attacks is Harry Potter. Critics of Harry Potter give two criticisms: Harry Potter contains witchcraft, which is forbidden in Scripture, or Harry Potter, while very much not actual witchcraft, might simply lead one to become interested in witchcraft.
Personally, I am, and have been for as long as I can remember, a Harry Potter fan. But I don't care if you're not. If you don't want to watch Harry Potter, don't. And if you have moral convictions for it, I actually say to you do not watch those movies. Whatever is not of faith is sin (Romans 14:23), and so while I don't believe it is a sin to watch it on its own, it is a sin for you to watch it because you aren't fully convinced in your own mind, as I am in mine, that it is a sin. The only time I will ever argue with someone over the morality of Harry Potter, therefore, is when they engage me first. Even on this ministry, I haven't written even half of the articles I could on the topic, because what I have already is enough.
With that being said, I have noticed a perplexing phenomenon recently. Right now, Guardians of the Galaxy 3 is all the rage. I haven't seen it myself, and I don't really plan to. But again, I don't care if you share that opinion or not. If you want to see it, go for it. But here's my problem. Several of the Christians I've seen praising the movie on their social media accounts, I've also seen criticizing Harry Potter in the past.
Hypocrisy is an ugly sin. Of course, it's one we all participate in to some degree. We're sinners trying to be Holy, and we're a Holy people who fall into sin; if we can call it a "fall". How can we praise God one minute, only to sin the next? Yet, if we say we have no sin, Scripture tells us we're deceiving ourselves, and the truth is not in us (1 John 1:8-10). I even find it internally conflicting, I was reading some of David's Psalms recently. In one Psalm, he calls for the demise of his enemies; those who hate him without cause, who lie in wait for his destruction. Yet, he expresses his joy that his own sin, that of murdering Uriah in order to steal his wife, has not been held against him. The Christian faith is the ultimate hypocrisy!
Yet, that is no excuse. We should wage war against sin! When we sin, Christ advocates for us, His very blood making propitiation for us. Praise the Lord. But Scripture is written to us so we may not sin. (1 John 2:1). Hypocrisy is our enemy. It is the fruit of the flesh, not of the spirit, and therefore it should be a casualty in every spiritual battle. We must cripple it. Behead it. Bind it in chains until its struggles are futile.
Now, as I haven't seen Guardians of the Galaxy 3, I do not know exactly which characters feature. What I do know is that it is a part of the Marvel Cinematic Universe (MCU), a collection of independent, yet interlinked movies, which frequently cross over with each other. That includes a set of movies involving one popular character in particular: Thor.
For those who don't know, Thor is a Norse god, son of Norse god Odin, and brother of Norse god Loki, both of whom also feature in the MCU. And of course, Scripture doesn't speak too highly of them. Scripture very clearly forbids following other gods, even saying that behind every idol is a demon, and under the law of Moses, following them resulted in death.
We therefore have two sins in view here: Witchcraft, and idolatry. Interestingly, as if Scripture wasn't already clear that the wages of sin is death (Romans 6:23), and that to stumble in obedience to the law even once is to be guilty with regard to all of it (James 2:10), witchcraft/sorcery and idolatry are often paired together as equally evil, and are said to bar one from the Kingdom (e.g. Revelation 21:8).
We're therefore faced with a choice. If we consider Harry Potter evil, we must equally consider the MCU evil (even if the movie does not contain Thor, as canonically, he still exists in the background within these movies). And that is fine. If it is the conviction you have, then keep it; watch neither Harry Potter, nor the MCU. This is a consistent option. I'll obviously refer you to my previous arguments for keeping that conviction to yourself, but keep it, nonetheless. May your walk with the Lord progress.
But my guess is those who are praising Guardians of the Galaxy 3, especially the not-so-casual MCU fans, probably won't take this option. So they'll start to rationalise their enjoyment of the MCU. But those rationalisations will be quite similar to the rationalisations of Harry Potter. Just as Harry Potter fans distinguish between the so-called "witchcraft" in Harry Potter and the actual witchcraft discussed in Scripture, MCU fans will distinguish between the Thor of Norse mythology, and the Thor of the MCU.
The "witchcraft" in Harry Potter is so unrealistic as to be literally impossible. The very instruments with which Harry Potter magic is typically performed are not even craftable. Every wand in Harry Potter contains a body part of a mythical creature: Dragon sinew, phoenix feather, or unicorn hair. Now, if it's impossible to do magic, why would the Bible forbid magic? And how on earth were people killed or exiled for doing magic? The simplest answer is that the so-called "witchcraft" in Harry Potter is not what the Bible is referring to. Therefore, we can safely distinguish Harry Potter from the witchcraft forbidden in Scripture, and so no verses against witchcraft apply to Harry Potter.
In much the same way, in the MCU, the norse gods, while they are still referred to as gods, are actually not gods at all. They are aliens from a planet called Asgard. They are certainly more powerful than human beings, and live a lot longer, but as I believe Odin says in one movie, "we're born, we bleed, we die". They're not gods. So maybe this is a justification for being ok with the Thor of the MCU while simultaneously opposing the myth on which he is based? Again, make your own mind up on this. I personally don't see a flaw in the reasoning, and I wouldn't dare accuse a Christian who thinks this way of sin.
But then comes the slightly punchier argument: What if Harry Potter leads to interest in actual witchcraft? This is actually somewhat possible. And it can't be denied there is quite a popularity gap between real witchcraft and those who actually worship Thor. There are, however, three main problems with this distinction.
The first is that even if it was true, it doesn't really matter; Scripture never forbids things based on what they could lead to. It never condemns taking a holiday because it could lead to the deadly sin of sloth. It never condemns eating a cake because it could lead to the deadly sin of gluttony. It never condemns displaying a trophy because it could lead to the deadly sin of pride. These are three deadly sins, yet Scripture only forbids the sin, warning us to guard our hearts, but never condemning what may simply lead to them. Thus, even if we argue that Harry Potter could lead to witchcraft, it's a moot point.
The second problem is that actual witches will give conflicting answers to this. To be clear, all witches will admit they have never seen, much less performed, magic like that seen in Harry Potter. But some will say maybe it's possible. Others, by contrast, will be utterly offended that people take it so seriously. That's just not what their religion is about. Some even flat out boycott J.K. Rowling for being a "TERF" (Trans Exclusionary Radical Feminist), because their version of witchcraft is fully supportive of the trans agenda.
But the third is that it's still hypocrisy. If we're talking about what it could lead to, the mere fact that nothing really prevents an MCU fan from having a heightened interest in Thor should be as much of an argument against the MCU as Harry Potter. If it's not an argument against the MCU, it's not an argument against Harry Potter. If it is, then go back to condemning both.
In the end, it really doesn't bother me which movies people watch. If you can find a firmly Biblical reason to avoid a movie, that's different. But if you want to watch Guardians of the Galaxy 3, for example, I have no quarrel with you, and I'll have a quarrel with those who condemn you. But what I must condemn is hypocrisy, and this latest trend is but one example of it from vocal opponents of Harry Potter. Harry Potter opponents have always had some degree of hypocrisy. I've always seen them pointing their fingers at Harry Potter fans while wearing Lord of the Rings t-shirts, drinking from Disney mugs, or holding a copy of the Chronicles of Narnia. Consistency is never their strong suit. But it's about time it was.
As Christians, division over something so trivial is not an option for us. God has made us all very different people, and thus we will inevitably have different interests. He forbids us from attacking each other over these things. Let us unite under His banner, being washed in the same blood, wearing garments from the same wardrobe, bowing to the same King. Silly squabbles like this are far more sinful than almost any movie, and when the world sees it, they laugh, and the devil rejoices. Let us honor God by holding hands in spite of our differences.