My problem with (some) atheists

Bashing Christians.
I have seen so many atheists attacking Christians for what they believe in and making memes about them that are just plain disrespectful.
It's bullshit. If religion makes a person truly happy you have no right to bash them. They are honestly more happy 99% of the time because they feel like they have purpose in life instead of just living to die.
Whenever I'm scrolling through iFunnys collective I never see them bashing Muslims, or Hindus, or any other religion. Just Christianty. 
Can someone please explain that to me?