A common fallacy in any religious debate is the straw man argument. That is when a debater attacks either an argument their opponent did not make, or a belief their opponent does not hold.
Christianity is a frustratingly easy religion to straw man, not only because atheists can make stuff up and claim Christians believe it, but because they don't even have to make it up. Over 2,000 years, a number of religions have evolved that claim to be Christian, and they believe a wide range of crazy things.
Pointing this out to an atheist will usually be met with accusations of the No True Scotsman fallacy, a.k.a. appeal to purity. This is when X (X, in this case, being Christianity) is selectively defined to exclude negative or inconvenient examples of X. The common example is that of a Scotsman claiming "no Scotsman would be a mass murderer", being shown a Scotsman who did commit a mass murder, then claiming that because this guy committed a mass murder, therefore he is not a true Scotsman.
I like to flip this one on its head by saying no true Scotsman was born and raised in Saudi Arabia to Arabian parents with no obvious connection to Scotland within the last 10 generations. Given the complete absence of Scottish connections, it makes sense to reject such a man as a Scotsman, right? Of course. A Scotsman should at the very least be affiliated with Scotland in some cultural way.
Just as it is acceptable to discount someone as a Scotsman if they have no cultural ties to Scotland, it is perfectly logical to separate a "Christian" belief from Christianity when it strays from the Bible, discount a "Christian" group as Christian when they do this consistently, or even say that a true Christian was not acting, speaking, or thinking in a truly Christian manner if the Bible disagrees with them at a given time.
But really, this whole situation is a huge compliment to Christianity. Christianity is so solid that atheists (or other unbelievers) need to lump us together with the crazies in order to stand a chance against us. They're so incapable of fighting Christianity that even once it has been pointed out to them that they have committed a straw man argument, they don't recant, they double down.
So, clearly unbelievers aren't as confident in their disbelief as they want us to believe. If they were, they would criticise Christianity for what it is, not what they want it to be. But what makes this even more ridiculous is what they are disbelieving in. Christianity isn't just so true that unbelievers often need to be dishonest in attacking it, it's so beautiful that I can't understand why anyone would want to attack it.
As Christians, we understand that we don't deserve eternal life. We deserve eternal punishment. This part is unpleasant, but what about the fact that God desires the opposite? Just because we deserve Hell instead of Heaven, God wants to bring us to Heaven instead of Hell. And how? Through the death of His own Son! Jesus, who knew no sin, took the punishment for the sin we know, and so all we need to inherit eternal life is to believe the faith no one can successfully refute. If you confess Jesus as Lord and believe in your heart that God raised Him from the dead, you will be saved. Why would you dedicate a second of your life to attacking that? Especially if your only method of doing so it to attack groups which, more often than not, don't even believe that?