Why do some athiests feel the need to slander christianity and make fun of it?

Not generalizing athiests in doing this, but I have come across many who do this. I understand that an athiest believes the idea of christianity to be absurd, but why can't some just respect the beliefs of others? Some christians as well, I understand, are not respectful towards other religious beliefs through missionaries and conversion and things like that. But my question is to athiests who mock the christian religion. What would they feel about a christian slandering atheism? There are people out there who look at athiest beliefs as absurd. But ofcourse, the athiest can back up their beliefs with science, leaving religious people to look like fools in not being able to support their beliefs with "facts". I feel like being a christian in today's world is like being gay before it was socially accepted. Anyone else feel this way?