This is highly offensive in so many ways. You have compared someone's sexual orientation to walking around on all fours. This is also absurd. Calling you a dog has nothing to do with your desire to walk on all fours - if that's what you want to do, by all means...I won't be the one telling you your two leggedness wasn't biologically meant to support that activity.we are not puppets, we each have control of ourselves and our actions, we do not choose our ethnicity but we choose our actions, so i wont agree that the two are the same. if you are going to define homosexuals vs heterosexuals by the mere existence of their desires, then we'd have to reclassify everyone in a similar manner (by what they desire rather than what they actually do/how they seem to us) and i doubt people would call me a dog for wanting to walk around on all fours because i desire to do so, or sympathize with me because the human world is not designed for such a method of travel, for that matter.
The biological argument is a poor one -- homosexual behavior and mating is found across species. This is well documented. The idea of homosexual desires being some sort of abnormal desire is really old and well abandoned by most of the psychological profession.
You define homosexuals and heterosexuals by the existence of desires. Many of us do not. Many of us including all of the scientific research being done on the 'gay gene' leads us to believe that that there is genetic basis to homosexuality. In that sense, many within the scientific world and outside of it believe you don't choose your sexual orientation.
Even if you don't buy the biological argument, please think carefully about the analogies you draw. If you believe that environment may have something to do with desiring someone from the same sex, that is still a lifetime of desiring people of your own gender. It is not an impulse that emerged overnight that you can deny or that you should deny. What is wrong with desiring another adult who desires you and consents to the relationship? Yet to see a rational argument against this.
Really? Biological parts not meant to go together? That's the best you could come up with? So not only is homosexual behavior wrong, anal sex is wrong, oral sex is wrong, any other form of sex that does not involve male and female parts in the missionary position must be wrong. Sad life for both homos and heteros now. Not only the above but also since clearly these parts were put there for procreation, in your view, then it must also be wrong for people who do not wish to procreate or who cannot procreate to have sex at all. Let's ban that too, shall we?
The only rational argument against gay marriage is that made by the gay community from within. Why would the community want to buy into and perpetuate an institution that is inherently flawed and has been used to oppress women for centuries? Having said that, I'd like everyone to have the equal right to reject the institution. Being granted the right to participate would be a first step in this regard.