It's a big straw man. It's incredibly easy to pick and choose the worst arguments for something then attack those as if you are destroying the real arguments. But it's disingenuous.

your sexuality is your identity'

This is a straw man. No one claims this. We all understand that your identity is composed of many different facets. You may be:

Black, English, British, a Chelsey fan, conservative, Christian, married, and straight. No one believes that when you choose to describe yourself as black you are claiming it to be your entire identity. We all understand you referred to yourself as being black because we were discussing race. If you are all of the things described above, you are all of them. The idea that homosexuals who admit to being gay are rejecting their identity in Christ is a straw man. No one actually makes that claim.

if it makes you happy it must be alright

Neither has any theologian who has come out in favor of marriage ever made this claim. This is another straw man. A claim that perhaps some uneducated lay people might make on random internet forums but that is not found anywhere in the literature when you look at what the pastors and theologians who support gay marriage are actually saying.

celibacy is bad for you

Yet another straw man. This has nothing to do with the question of whether the scriptures forbid homosexual relationships or not. This is yet another thing "random internet guy" might say, but which you won't find put forthy by any of the pastors or theologians who support gay marriage.

suffering is to be avoided

The last straw man in your list. Again...no one makes this claims.

Its incredibly easy to make up your own arguments to attack and then proclaim yourself victorious. But in doing so, all you've managed to show is that you lack any understanding at all of what the other side actually believes. Or worse yet, perhaps you do know and are being disingenuous by picking and choosing the worst arguments you can find and attacking those instead of engaging with the real meat.

There's no meat to what you provided.

Given that the rejection of gay sexual activity had been a feature of every church everywhere

I suppose if you are a Catholic it might be acceptable to think this way. But for the rest of us, the authority does not lie in our traditions but in the scriptures. If you want to outlaw something, you need to show with scriptures that you are not creating needless rules for people. Appealing to tradition as you just did is improper. The tradition is irrelevant, if you want to show something is wrong you need to show it is wrong, you can't just assume that it is wrong and challenge someone to prove it isn't.