This is a strange answer, because such quasi-defenders of gayism cannot be elevating human choice (or the exercise of it) to an absolute; they cannot be preaching that people can do anything and everything which fancies their desires.
What if someone chooses to mass-murder a town?  What if someone chooses to be a child-abuser?  What if someone chooses to steal?  (In fact, what is someone chooses to beat up homosexuals?)  Will we merely shrug our shoulders and say, "It's their choice"?

Merely stating the FACT of choice in no way addresses possible OBJECTIONS towards that choice.  And the Christian objection towards homosexuality is primarily (though maybe not exclusively) moral in nature i.e. gayism trespasses certain moral boundaries and/or represents a breaking of a moral law set by an Almight Law-Giver.

Homosexuality - in the Christian worldview -  is a personal transgression against a Meta-Person, very much like a son choosing a policy of hate and distrust towards his father.  The deed is 'wrapped up' in and symptomatic of the personal affront, disrespectful attitude, indifference or hatred towards the significant Other in question.  This is not 'homo-phobia'(?) in any way but rather a concern for the integrity of personal relationships in our world, especially of that with our Heavenly Father, the Maker and Saviour of us all.

Individual repulsion isn't the issue here, and never should be (in fact, try to imagine a morality based upon what does or does not repulse us!).

One might object:
"Hey, Al, wake up!  There are MANY people nowadays who do not believe in God (or who at least don't believe in the God whom Christians speak of, much less that His morals 'apply' to them) - so how is sprouting 'Christian morality' relevant to this discussion?  Why talk about standards which many people do not feel compelled to uphold?"

Good question.  Putting aside the fact that the major world religions more or less object/question homosexuality (and the suspicion this might suggest for any 'new' belief which supports it), I'd like to respond in two ways:

1.  A Moral Framework is REQUIRED to maintain the integrity of any action (incl. homosexuality)

Christian principles form the framework by which to judge an act/lifestyle as Right or Wrong.  One reason why we can celebrate that which is Good/Permissible is because we can clearly distinguish such activities from that which is Evil/Non-Permissible.  On the other hand, those who say that homosexuality is permissible have to explain what they consider to be not permissible and - most importantly - the arbitrating criteria by which these two categories are distinguished.

In other words, what is the standard or criteria for judging between good and evil?  Because failing this, complaints AGAINST those who would call homosexuality immoral (e.g. Christians) lose a valid basis.

Why do we complain about people who say that homosexuality is wrong if we ourselves have yet to establish a coherent Right/Wrong standard?

In order to say "Homosexuality is okay", we need to first have a coherent basis for saying that "Some things are NOT okay".  This also helps avoids the obviously nonsensical - but nihilistic, if consistent - "Everything is okay" (I think Nietzsche saw this more clearly than most).

The bottom line here is that I don't think we can be taken seriously if we object to charges of immorality without FIRST having developed and presented foundations by which our values/morals are upheld. The 'tuff' part here for most liberals would then be that of defending this entire edifice and justifying why anyone should comply to this new moral.
 

2.  A Moral Framework is often PRESUMED experientially by everybody anyway(!)

Many times when Christians teach that homosexuality is wrong, there is that occasional snap: "Don't you DARE stuff your morality down other peoples' throats, you Bible-thumping fanatic!"  *smile*

Notice that there is an inherent moral law inside that statement, which goes something like:  "We should not impose our own understanding of morality upon others."

But why not?  Says who?  And even if more than half the world's population feels this way (thus making it 'generally accepted'), why in the name of all that is purple should I subscribe to that 'law'?
Fact is, the modern liberal attitude of resisting traditional forms of morality still has to presuppose the 'moral validity' of just such a resistance.  And to expect everyone else to agree is itself an 'imposition' of one's own morality.  For why should a traditionalist follow the moral command of the liberal to stop preaching laws of old?  Or phrased another way:  Why should the traditionalist have the liberal's laws - one of which is to not impose traditional morality - 'imposed' upon him?

So we see that liberals are just as guilty of 'shoving' their own brand of morality down other people's throats when they voice this very complaint.
 

If nothing else, I hope this essay serves to remind us that this isn't merely a matter of 'doing whatever we like'.

Those of us who insist on defending the practice ought to develop a far stronger reply than merely stating the obvious ("The choice is theirs" - whose else could it be?), the inconsistent/dangerous ("Let them do whatever they want" - are we sure?) or the irrelevant ("Quit the homophobia, will ya?" - done that, let's stick to the issue... *grin*).

"Unless we stand for something, we will fall for everything."
 

AL