1. That Christianity is a preference, a choice.
You don't say eating is a preference, do you?
2. Anyone who calls himself/herself a Christian, is a Christian.
You don't believe I am a sandwich, do you?
3. Christians are homophobic, racists, discriminating bigots.
Successful abolition of virtually all various bigoted practices are initiated and inspired by Christians, though there are fringes of wannabes from time to time, but merely wannabes nonetheless.
4. God only loves and forgives. He does not hate, punish, etc. or else He is not God.
If that is so, I supposed a coin that has both a head and a tail is not a coin.
5. Sin is doing something that is hurtful to others.
Saying that is already hurtful to some.
6. Christianity is against science, open thinking.
Those who advocate this already, certainly, admire a lot of Christian scientists, so I'll give them a short break here.
7. Christianity, Islam, Judaism, etc. are not mutually exclusive.
Is this statement mutually exclusive?
8. Christians think themselves sinless.
This is often used by those who wish to find a way out of their own faults. But one's hypocrisy is not an excuse for another to follow.
9. Christians are nice.
This is a bit insulting. It is better to be good and kind, since the original meaning of nice is foolishness.
10. Christians share the Gospel/convert others for their own gain, power, wealth, etc.
Despite many unfortunate convincing experiences, the truth that debunks this, if any, however hindered, must certainly be more precious than anything else.