So far I have looked at the Bible and not found any reason to object to gay sex in and of itself (as with any activity it may be sinful depending on the other circumstances), I have looked at values and found them of limited help, and in my initial list of ways of looking at this I tackled Tradition. That leaves Consequences and Reason from that initial list.
I tend to dislike consequences as they are so difficult to predict. However, I think it would be true to say that Gay Sex has been going on for rather a long time, so any attempt to blame the changes in society on it are doomed to failure; attempts to discuss the health impacts on the participants lead us to the health impact of other behaviours (eg smoking); and in fact it is difficult to define gay sex other than as activity between people of the same gender, as straight couples can, and some do, engage in the same behaviours.
So on to reason.
One of the arguments against gay sex is that it is not within the context of marriage (note: this is not about the activity, but the context), and yet those who object to gay sex in this way will often want to deny same sex marriage. Why? (I know the argument that if the behaviour is sinful then institutionalising it is bad – but that doesn’t define the behaviour as sinful).
Another is that being gay is a choice, and consequently it is sinful because if we are all made in God’s image then acting outside of that is sinful (not sure where the argument that God is straight comes from though). However, without the argument of God’s sexuality the argument falls. Despite this there have been debates about whether there is a “gay gene“, with the existence being used to argue that if God made gay people gay then it is OK; but why is God restricted to making people by genetics?
Finally, the only difference between gay sex and straight sex is that straight sex can lead to pregnancy (at least in theory). Roman Catholic theology requires that each conjugal act be open to conception, and this argument would appear to clinch it – except I don’t hear many priests condemning contraception in the same terms as they will condemn gay sex, and any church which allows contraception immediately loses this argument!