if the majority of people were athiests

This is what it would be like, if the majority of people were athiests.
ATHIEST KID: Mom, I'm going to go fuck a hooker.
ATHIEST MOM: Okay, son.
ATHIEST KID: Afterwards, I'm going to go smoke pot with my friends, since it's "not addictive."
ATHIEST MOM: Okay, come home soon!

The athiest kid leaves the room. The father comes home from work several minutes later.

ATHIEST DAD: Hey!
ATHIEST MOM: Hi, honey! I'm pregnant again. I guess I'll just get another abortion, since "fetuses don't count as human life."
ATHIEST DAD: Okay, get as many abortions as you want!
ATHIEST MOM: Oh, and don't go in the bedroom.
ATHIEST DAD: Why not?
ATHIEST MOM: There are two gay men fucking eachother in there.
ATHIEST DAD: Why are they here?
ATHIEST MOM: I wanted to watch them do it for awhile. They just aren't finished yet.
ATHIEST DAD: Okay, that's fine with me!

Suddenly, their neighbor runs into the house.

ATHIEST NEIGHBOR: Come quick, there's a Christian outside!
ATHIEST MOM: We'll be right there!

The athiest couple quickly put on a pair of black robes and hoods. They then exit the house, and run into the street, where a Christian is nailed to a large, wooden X. He is being burned alive. A crowd of athiests stand around him, all wearing black robes and hoods.

RANDOM ATHIEST: Damn you, Christian! We hate you! We claim to be tolerant of all religions. But we really hate your's! That's because we athiests are hypocritical like that! Die, Christian!

THE END

Scary, isn't it?

This seems more like some sort of nihilism to me, though Nietzsche would claim atheism leads to nihilism. It could become reality though, and I do not see anything wrong with that.

You see, you try to paint up a terrifying scenario, but since you are the only one believing in silly christian morals (wrote into a book by various states seeking to control their peoples) it only appears repelling to you. And for atheist/nihilists to team up with each other and systematically fight christians is just silly.

Still, just because people don't adhere to a religion doesn't mean they will work out their own ethical values (or more often, sadly, continue to adhere to the same ethical values enforced by the state and church).