Discrimination is not necessarily bad. I discriminate on the kinds of foods I eat, on the programs I watch, and what movies I let my kids see. In fact, we all discriminate. We all have criteria by which we judge what is and is not acceptable. I discriminate against child molesters, and I will not let them be with my children unattended. I discriminate against various theological teachings that contradict the Bible. I discriminate all the time and so do you.
In his Word, God has condemned homosexuality (and many other things) as sin (Rom. 1:18-28). But my agreeing with God that homosexuality is a sin is not the same as discriminating against homosexuals. I have no problem working with homosexuals in a secular environment. I have no problem with homosexuals being my neighbors. I have no problem with working out at the gym with homosexuals. In things like these, I don't discriminate.
Likewise, I would agree that someone should not be fired from a job (in the secular realm) because he or she is homosexual. I think that is wrong, not because it is based on sexual orientation but because we should treat everyone as equally as possible.
Having said that, because of my religious beliefs and my right to express them, I would not promote homosexuality, nor would I change my preaching and teaching so as not to "offend" those who think that having sex with people of the same gender is perfectly normal and morally acceptable. The fact of the matter is I'm offended by their lack of moral sensibilities. But no one seems to be concerned about how I'm offended or how I feel about the intrusion of homosexuality into society, TV, the movies, etc. But I digress.
To say that condemning homosexuality is wrong is a statement dealing with morality, not with legality. There might be various laws for and/or against homosexuality, but saying that condemning homosexuality is wrong is a moral issue. My question then would be by whose standard is something right or wrong, and what justifies that standard as being valid? Yes, I know, a homosexual can ask me the same question, and we could debate it but that is another conversation.
If an atheist were to say that condemning homosexuality as a sin is morally wrong, then on what basis does such a statement gain its moral objectivity by which a blanket condemnation can be made? If someone says that the majority of society determines what is morally right and wrong, that is called the fallacy of Argumentum ad populum. Just because a majority of people think something is right or wrong, doesn't make it right or wrong.
So, when a person objects on moral grounds to my moral objections or other Christians condemning homosexuality as a sin, he has no objective moral basis by which he can make his objection. At best, all he is doing is giving his opinion, and it would be arrogant to think that his opinion is the standard of morality for everyone else.
However, when I, or any Christian, make a moral objection to homosexuality, we do not do so on the basis of our own opinions. In and of ourselves, we have no right to declare homosexuality to be sin. We are simply reiterating God's opinion as He has unequivocably expressed it in the Bible. Homosexuality is sin not because we say so but because God says so. More importantly, if Christians begin to accept the lie that homosexuality is not sin, the only avenue through which homosexuals can hear the truth about how to avoid an eternity in Hell will be closed to them. Millions who are engaging in a behavior which God calls "abomination" (Lev. 18:22, 20:13) will be subject to his wrath, and many of them will never have had the opportunity to learn of the only way to avoid it--through faith in Jesus Christ and repentance.
Condemning homosexual practice as a sin is not discriminatory in a legal sense, but it is one in a spiritual and moral sense, and as such, we are free to condemn it.