Most people aren't gay, which makes it easy to attack this particular sin, because this sin will never become their problem. People can keep on attacking this sin knowing that they will never commit this sin themselves. Some other sins, for example adultery, lying, dui, violence etc can easily be more dangerous to attack, because there is always this theoretical chance that the accuser can actually end up sinning him- or herself. Not so when it comes to homosexuality.
So, when some people needs to judge, they pick the gays, because that's a safe space.