***Get's somewhat explicit in discussion of what sex is 1/2 way though***
There is a reason that homosexual "marriages" shouldnt be allowed legally and that is that they are impossible.
Marriage is something God created, not the state. Marriage is defined by God, not by legislators. Marriage involves, by definition, a bridegroom and a bride. Also, the very definition of bridegroom and bride are even laid out and involve the definitions of masculinity and femininity. What it means to be a man, and what it means to be a woman, are intimatly tied in with this question, and part of this involves physicality. One thing that makes women distinct is not only their ability to receive (compare various 'private parts' of men and women to the definitions of masculinity and femininity), as well as the ability to reciprocate at the same time, and also to bear fruit.
Basically, a homosexual 'marriage' isnt possible because it defies the very definition of marriage. The vows include giving yourself totally, faithfully, freely, and fruitfully. It's not that we shouldnt allow them to get married becasue they are a lower class (which they arent), because they sin more (which isnt necessarily true, but it can be case by case), or whatever, isnt the point. We shouldnt allow it in law because it is impossible in God's eyes.
Demoting and demoralizing those with an attraction is wrong. They have a disordered desire, and are lost and confused. They do not need to be discriminated against, but rather prayed for helped in any way that they wish. It is true that there are many people with a homosexaul attraction (SSA) who live chaste lives an strive for purity in heart, mind, and body. You can have both SSA and be a Christian. The two are not necessarily contradictory.
Now, why are homosexual acts (aka 'sex') in itself sinful? It is simple. Some call it sex, but it isnt. It is more like foreplay. Sex by its very definition is fruitful and unitive. While anal 'sex' is unitive, it most definitly isnt fruitful. The same goes for oral 'sex.' While they are inherantly sexual, in that they imitate the TRUE form of sex, they arent really sex for this reason. True sex, which is better called the marital embrace or one-flesh union, is unitive and fruitful (meaning there is an openess to God and whatever blessings He may bestow through conception). Anything which does not contain these things is a desecration of all things holy and true. Anal 'sex' and oral 'sex' are cheap rip offs which were not created to draw us closer together, but rather to deviate from the way God created things. Now I am not saying these things are inherantly wrong, but can be. If used by themselves, apart from the TRUE sex, they are wrong and immoral. If used more as foreplay, with the FULL and WILLING consent of BOTH partners, then there is nothing necessarily wrong with it. But they should not be the sought end, for then we are merely settling for an imitation. This also doesnt mean that they are okay outside of marriage. In fact, they are wrong outside of marriage because they are so sexual, and involve going beyond chastity of the heart and mind and body simply because of the level of intensity and closeness that they involve. I said they were more like foreplay for a reason. Foreplay doesnt exist on its own, but is a "fore" to something. This is why they are also for marriage alone, if at all.
Nonbibilical views? Its not like they matter since our very constitution is quite biblical, but Im sure I can come up with something.
Lets see, you could talk about what sex really is. Keep in mind, that if we are going to talk about what is natural, then we have to throw out ALL contraceptions, all outside lubricants, EVERYTHING, and simply talk about the body, functionality, etc. Outside innovations (such as spit) dont count. If you want to speak naturally, then we must also speak functionality, which speaks not of innovation, but the way our bodies are.
For example, when a man and woman have sex (and I am talking real sex, not anal or oral or anything like that), there is a naturality to it in that there is a natural lubricant, and that the walls of the ****** basically 'grip' the man's *****. [Or so I am told. Correct me if I am wrong.] Sinec this is a natural thing, it shows that the ****** is not just made for excretion of certain bodily materials, but also receptivity. Also, it is natural in that it is fruitful, and purposeful evolutionarily (aka the continuation of the species) speaking.
Anal sex involves the rectum, which is dirty and can cause disease because of such. There is nothing about the rectum which shows that it was created for something to be inserted into. As the ******, it does not grip the ***** being inserted into it. It also has little if any lubricant that is created during intercourse for that purpose. Also, anal 'sex' is not fruitful. This means that evolutionarily speaking, no homosexual species would survive on their own, and would die off, if it weren't for others. And any group of homosexuals in a species would have to rely on 'converts' so to speak (although the psychology does not in any way suggest that it is that simple). You could also introduce psychological arguments, such as that since the 'sex' isnt face to face, it involves and creates an environment for objectivity, which is not embodied in true 'love.' (But then, the definition of love that I have is a Christian one which involves the highest good for the other person.) Also, another note. Sex between a man and a woman brings both to [bless and do not curse][bless and do not curse][bless and do not curse][bless and do not curse][bless and do not curse][bless and do not curse] in the one act. Anal sex between two men does not do so unless there is further or other stimulation (generally speaking). For two women, the argumentation is easier, for they dont even having something to penetrate the other with sexually, but must rely on the use of a) fingers, or b) their tongue. The tongue, functionally speaking, would be longer if it was meant for this use. Fingers, well, we wont go there. Fingernails are not something conducive to a pleasureful state, and more likely to harm the other person when inserted (especially since women generally have longer fingernails).
I hope this helps, was not too graphic, etc.
God bless