In fact, I translate what you just said to...
"I believe that sex is of more relevance than sexual orientation when it comes to determining rights."
Can you make an argument on that basis without clearly trying to diminish sexual orientation as a deformity or mental defect?
In fact, I find it so disconcerting that you would compare sexual orientation only to mental illnesses and deformities, even while acknowledging that they aren't the same, that I feel compelled to provide a different comparison.
Let's compare sexual orientation to hand dominance. If you think about it, they have a lot of similarities. For one, within any population there is a certain percentage of people who are right handed, a certain percentage of people who are ambidextrous, and a certain percentage that are left handed. That is due in part to the fact that some genetics come into play in determining hand dominance. No one gene determines whether someone is left or right handed. Similarly there is a certain percentage of people who are straight, bisexual, and gay within any population, which demonstrates that there are also also genetics that come into play when it comes to sexual orientation, and there is also no one gene which contributes to it. (In fact, in sheep, approximately 8% of any given population of rams will only seek other rams for sexual purposes.)
A certain degree of socialization also comes into play when determining hand dominance. Consider back in the day when many religious groups considered the left hand to be the hand of the devil and as a result if a child showed preference for that hand, they would try to alter that child's hand dominance, usually by means like sticking it into burning sand or whacking it with a ruler whenever they tried to use it. Similarly there are socialization factors involved when it comes to sexual orientation as is evident by the fraternal birth order studies which show someone who has an older brother who is gay is 33% more likely to be gay themselves. And of course, religious groups have historically tried to change sexual orientation.
Now lets consider something. You can choose which hand you use. Right now you have the free agency to pick up a pencil with your non dominant hand and try to write your name. Of course if you do so, you will probably find it unnatural, strange, and difficult. The same is true with sexual orientation. You have the free agency to choose who you sleep with. Of course if you are straight and you choose to sleep with someone of the same sex, then you might find it a little unnatural, strange, and difficult to do so. The same is true of being gay and trying to sleep with someone of the opposite sex.
Now it has been found that trying to change someone's hand dominance can result in lasting psychological damage to that person. As a result, virtually no psychologist would ever attempt to change a person's hand dominance. Even if such a person came into their office feeling really guilty and ashamed of using what their culture considered the wrong hand. However, some psychologists have no problem trying to change a person's sexual orientation despite evidence doing so could be harmful and result in lasting psychological damage. That is the position of such organizations as the American Psychological Association and the National Association of Social Workers.
Now obviously hand dominance is not exactly the same as sexual orientation. Human sexuality is far more complex than that, but it certainly is a far fairer comparison than comparing sexual orientation to deformities and mental defects. Primarily because being gay doesn't diminish your ability to function. You might argue procreation, but gays do have kids, either from adoption, surrogate, or marriages where they have tried to pass as straight. And many straight people simply choose not to have kids. So there really is no justification for the comparisons you made.
And at the matter at hand, it would make no sense to deny people who are left handed the right to marry. Probably not anymore so that denying people who are gay the right to marry. Arbitrary facts of life, such as your hand dominance, sexual orientation, and even sex should be treated as just that, arbitrary. People have more in common by just being human beings, than they are different as a result of things like sex and sexual orientation.