LegendBegins said
BecauseA) It's trueB) It's more fun to believeC) It gives me an edge in case I ever need to use it against her. Why do you even care? Would you stop being her friend for being a lesbian? Would you attack her just because she likes girls more than guys?
They care because they're refuting a lie. It wouldn't matter what the subject was, if it's untrue they will refute it.