Down's Syndrome is a mental-biological defect whereas being gay or lesbian is perverted choice, a deviant 'lifestyle' that are the result of different influences perhaps early in childhood.

One of the clearest indications that homosexuality isn't 'normal' is that the parts don't match, and one cannot reproduce through a homosexual union. Nature always wants to carry on its seed for the purpose of species survival, and homosexuals and lesbians are unable to do this.

No 'gay gene' has yet been proven, although homosexuals often pretend as if it has.

Since they cannot reproduce, they must recruit. It's another indication that the movement is not biologically-based and runs counter to the natural order of things. The parts don't match and one cannot reproduce through the act.

I fail to see how it's a choice?

There is no concrete evidence that homosexuality is biological or genetic. It's one of a plethora of sexual dysfunctions and deviant behavior that humans engage in, and a sane society neither 'celebrates' it nor condones it because of the moral effects on society, including the break down of the family structure.

So should we do away with kissing, caressing, fellatio etc?

Whatever one chooses to do with their heterosexual spouse should be kept private, and no cultural movement should ever be created around one's sexual proclivities - and yet this is precisely what gays do.

No "intelligence gene" has been found so far too, but that doesn't mean it isn't there

I'm sorry, but there is far more evidence and rational for intelligence being genetic and having a biological foundation than gay sexual practices. I'm not denying early childhood influences and cultural pressure, but that's not the same as it being genetic in origin.