I am not trying to deny them a right. I am objecting to their usurping of a tradition that does not belong to them.
Who owns a tradition? Did you personally invent marriage? If not, why do you believe you have a right to 'own' it, and prevent others from participating?
The problems are that:
1. It gives them access to legal rights to adoption which I don't think they deserve
What makes someone 'deserve' adoption, and why does no homosexual couple deserve it?
2. The underlying political agenda is to use the hijacking of the marriage label as leverage to get society to view homosexuality as normal when I think it is not normal; it is a defective manifestation of the human sexual instinct.
You have it exactly the wrong way around. Homosexuals and their allies could not conceivably 'hijack' marriage without already having majority support.
3. If it really is just about legal rights then amendments can be made to selected bits of legislation to extend the rights in that legislation from married couples to homosexual partnerships. But it is about more than legal rights. It is about the political goals of a minority.
That is eye-bleeding nonsense. 'Selected bits of legislation'? You cannot believe the words you've typed.
At the end of the day homosexuals are doing quite well just getting society to accept and tolerate their behaviour within certain limitations.
Yes, better that homosexuals are reminded of what the proper moral reaction is -- to execute them. There are countries that still do that, I'm sure you'll be glad to hear.
Obviously we see homosexuality in different ways.
You see it as a normal expression of human sexuality and I don't. Science cannot tell us yet who is right but one day it probably will be able to provide a causal explanation of homosexuality.
Why would a causal explanation (or the absence of one) matter?
The icky argument is that the vast majority of society is heterosexual and heterosexuals find homosexuality icky. We now tolerate homosexuality but that is not to say that we want it rammed down our throat (for want of a better metaphor). In return for tolerance and legal protection homosexuals could be reasonable about it and keep their business discreet. That is my honest view despite how jarring it might sound in the current politically correct atmosphere. Political correctness isn't simply about a majority view; it is about a false agenda being pushed to assert the notion of equality as an abstract political goal even though the things being compared are not equal.
If anything is rammed down people's throats, it's heterosexuality. You can't pick up a book or turn on the television without relentless reminders of it.