The arguments that I have heard against Christianity fall into a few largely absurd categories (Yes I know I don’t have time to cover them all):
1) Christians have done some terrible things over the centuries Hmmm? So, lots of individuals have done terrible things for a variety of reasons, What does that have to do with the veracity of Christ’s message? This is outright propaganda, because these people rarely want to talk about humans being human and subject to this type of thing. More dangerously, the assumption is there that if we were to “do away” with some particular groups access to power, then we’d all be much “safer”.
2) You can’t prove that God exists. We’ve gone over this ad-nauseum. There is no evidence either way. The only thing that atheism tries to assert is that people should start from the position that God does not exist and demand proof (of something for which there is little if any empirical proof). That's a tricky little rhetorical joust , but most people don’t start there, nor are they required to. It’s be like a Christian telling a Muslim “Okay first you have to accept that Christ is the Son of God and demand proof that he is not”. Muslims and atheists alike would cry foul and rightly so. Even if you claim a neutral stance, (ignoring the paradigm that most people are theists). Telling people that they should think like an atheist about their religions will likely get you nowhere. If you embrace that paradigm then you’re just another worldview having to support itself like all the others.
3) God does some really terrible things. I like this one. It amounts to an outright character smear on the Almighty. Don’t go ‘round telling people that God shouldn’t care about your beliefs if you are slandering him. Here we have to remember that you do not have to have any particular knowledge of scripture to tell people how much you know. As long as you keep up invective after invective and don’t let anyone pin you down on one story you’re safe. I’ve pinned a few down over the years. It usually goes something like this:
“God had no right to destroy Sodom and Gomorrah, all they were doing was having sex”
“Really? So you advocate gang rape as a social norm?”
“Huh? No!”
“Have you read the story? They clearly demand that Lot send his guests out ‘So that WE may know him (in the Biblical sense) as is our custom’ That doesn’t sound very nice”
“Well okay the adults had it coming, but what about the children?”
“What Children? There are no children mentioned in the story at all, and they are specifically mentioned in other towns and other stories. Remember these are towns where a grown man was a risk walking down the street”
“Well, um, There are lots of others stories where God is mean I could go on and on”
“Yes, I’m sure, Well Good day to ya’”