I get what you're saying.

About 4 years ago I was a Christian who said the same stuff about Homosexuality.
But look at it this way.

Homosexuality is a sin.
But Heterosexuality isn't a sin.

That ultimately means one (Hetero) is better than the other (Homo) and that Heterosexuality is therefore a true and right sexuality while the others are flawed and wrong.

It's the same as saying being black is a sin, but white isn't. 
Even if the being black was wrapped up with everything else, you'd still look at that and go "That's pretty unfair and discriminating to Black People".