In Christianity, sin is the biggest problem that needs to be solved. It is the thing that separates us from God, preventing us from having fellowship with Him and ultimately forcing Him to judge us, condemning us to death both physically and, after that, eternally. Aside from being the thing that causes God to reject us, it's also the biggest thing that causes us to reject God.
It's quite common for unbelievers to object to God based entirely on His morals (or their misunderstanding thereof). For example, many atheists look at the harsh judgements God executes against sinners in the Old Testament, from the flood to the twin cities of Sodom and Gomorrah to Egypt to the Canaanites, and everyone else besides. But it's not just the harsh judgements God executed in the past that bother them, but also the current morals God requires us to follow.
When I was new to the faith, I knew a young girl who said she could never become a Christian because she liked alcohol too much. I understood her objection. I'd also been raised with the idea that Christianity is opposed to alcohol, but other than the tiny bit of Vodka I'd tried, which I really didn't like, I'd never had any alcohol in my life, so it didn't seem like an obstacle to me. But having converted and studied the faith a lot more since then, I understand that it shouldn't have been an obstacle for her either. Why? Because Christianity isn't opposed to alcohol, but to the abuse of it.
This should have been evident from the fact that Jesus, who knew no sin, turned water into wine. As you dig deeper into the Bible, you find passages like Romans 14, Colossians 6 and 1 Timothy 4, all of which put forward a positive image of any dietary lifestyle as long as it is done with thanks given to the Lord, even saying that those who have a more liberal view of food, drink and festivals have a strong faith, whereas those who believe we are limited in what we may and may not consume are weak in the faith. So of course we can have a few drinks. Nothing in Christianity says we can't consume alcohol.
But of course, there are limits. Christianity does condemn drunkenness. So does the Cosmic Killjoy argument still stand? Not really. Although a slight buzz may be pleasurable, drunkenness can cause humiliation, serious harm, and even death. This is especially true in the modern era, where you can not only make a fool of yourself, but also go viral overnight for doing so.
Too much alcohol drastically affects your mental faculties. Even a few drinks can alter your ability to walk, or open doors, and of course there's a reason there's a legal limit to how much you can have before it becomes illegal to drive. I remember at a Christmas party, a woman I was with was drunk before we even got to the pub. She was told off twice for dancing in front of the stage where there were performers, and she repeatedly told me, in front of her daughter's boyfriend, that she would prefer her daughter date me. A few years previously, while drunk, she attempted to kiss me.
A common theme when I practice Krav Maga is the bar scene. Drunk people are more likely to cause problems, and of course it weighs heavier on your conscience if you seriously harm a drunk person, even in self defence, than a sober person, since the drunk person has less of a grip on reality. Drunkenness makes one more vulnerable to abuse, especially if you're an attractive female. It can even be considered rape to sleep with a drunk person. All of this stops just short of death, but even death is a possibility. Alcohol has caused many people to do stupid things, leading to death. Even alcohol itself can be a lethal poison if consumed in large quantities.
And so we see that there's a reason God speaks against drunkenness. It's not that He disapproves of alcohol and wants to stop us enjoying it, but rather He wants to make sure we get maximum enjoyment out of it. He wants us to have the pleasures He created alcohol to give us, but He doesn't want us to suffer the painful consequences alcohol abuse brings.
Alcohol is second only to sex, another thing unbelievers typically believe God hates. But the truth is, God doesn't hate sex. He invented it. In fact, after God created Adam and Eve and said "Be fruitful and multiply" (Genesis 1:27-28), Moses tells us He looked at everything He had made, including a sexually intimate human couple, and called it "very good" (v31). This is the first time, after six times merely saying "it was good", that God says everything He made was very good. In other words, sex was a part of God's perfect (Deuteronomy 32:4) creation.
But just like alcohol, God has a few rules about sex designed not to remove our enjoyment of it, but to maximise it. And again, we look around the world and see the trouble that abusing sex brings. We see children living with only one parent present in their lives, assuming their mothers didn't slaughter them before they took their first breath. STDs and STIs run rampant (gay sex increases this danger). Women are enslaved by "pimps", and men turn into complete pigs. Relationships become empty, lacking and real depth, because all we really want is one thing: sex. And when the sex gets boring, off we go to the next person, who again must satisfy that one need, but they won't be able to. At least, not for very long.
This isn't how sex is supposed to be used. It should be the icing on the cake, so to speak, of marriage. We should want sex with our spouses, but we shouldn't only want sex from them, or even for them. Whenever we stray from God's design, we end up with all of the above, and more. But if everyone on earth obeyed God to the letter with regard to sex, all of that would be reduced, if not completely eliminated.
And of course there's a lot more we tend to disagree with God about. We often see His commands as a restrictive fence to keep us in, but in truth it's a defensive wall to keep the horrors out. Think of it as like a trip to the zoo. There's not a single animal I wouldn't love a close encounter with, and fences all too often make it difficult to get a good picture, but as much as I'd love to live in a world where the fences weren't there, the fact is they are 100% necessary. I wouldn't be happy to go to a zoo where the animals weren't at least slightly restrained. In fact, if it meant I got to keep my insides inside myself, rather than inside a lion, I would volunteer to get into a cage. And so, as G.K. Chesterton says, never take down a fence until you know why it was put up.
In Christianity, we serve a loving God. His laws weren't put up to withhold life's greater joys from us, but to withhold us from life's greater turmoil. Remember this: When Satan tricked Eve, He did so by making the guard rail look like a prison wall. "You will not surely die", he said. "God knows that in the day you eat of it your eyes will be opened, and you will be like God, knowing good and evil." Oh, how dare He? How dare God withhold from us this great gift?
And it turns out, Satan wasn't lying. Before blocking off the tree of life, God said "Behold, the man has become like one of Us, to know good and evil." Adam and Eve got their wish, just as Satan promised, but with severe consequences neither of them wanted, neither did God want them for us. Thus began a 6,000 year war between God and man. A war in which Satan continues to use the same strategy: Question God's word, make Him seem like a thief and a tyrant, and assassinating us soul by soul.
But not forever. The enmity between God and man is not irreversible. Far from it, because there was a man who never once tried to seize from God what was not His. This man never tried to take down the fences, He even made a few repairs and improvements to them on God's behalf. That man was Jesus Christ, the Son of God in human flesh. Because He was sinless, He was a worthy substitute, able to take our place as the object of God's wrath against sin. His message? Repent of your sin, believe in Him, and receive the free gift of eternal life. This will mean coming back inside the fence, but to the redeemed sinner, this will not be a problem.