Let's go with a sin that just fills this site continuously, (me included, but not you.) Haughtiness.
Would you prefer we were so proud of our haughtiness that our we rename this sight "Haughty Christian Chat?" Would you want to come running to such a site? Do you see how that just overflows with God's message? Do you think I should have haughty buttons so everyone knows how haughty I am? Should I be proclaiming "all sin is equal, therefore I'm cool being haughty and you should be too?"
I do agree homosexuality is no worse nor no better than any other sin, but to proclaim proudly that they are homosexuals, really does say they think they're better than God, so he has no problems with them being homosexual. And that is their message, which is the problem with calling them Christians.
I've known, and know, Christians who have to fight that sin every day of their lives. It really is a tough struggle. But I know they are Christians because they know it is a sin deeply enough that they struggle with it. No different than me and haughtiness, but completely different than proudly proclaiming a sin as not-a-sin. Badge-of-honor. That's the difference.