The contemporary take on gender (being accepted in academia-especially in principles like psychology and social science) is that it differs from sex, where sex is your assigned "male" and "female".
Perhaps, regardless of that, it is still something grounded in biology. albeit it harder to understand the human brain/mind then to observe ones physical bodily features as such. And I don't necessarily agree the contemporary view of gender is grounded in the right things. I often see this as one area where ideology (in this case the LGBTIQ one) colours sound judgement. And even if you distinguish between gender and sex, and it is not as if these two things are disconnected concepts. Ones sex should in my view, determine their gender, and ones gender should conform to their sex (not the other way round as in contemporarily). (That is driven by ones view of what it means to be human)
However, in this case when I refer to constructs I'm referring to the changing construct of marriage to being defined additionally as same sex.
But the right to marriage and intimacy is something I and many people believe is owed to same sex couples as it is owed to heterosexual people. We can agree to disagree, and you have the right to you own view but Australian (and- increasingly- other countries) legislation on this has changed to accept same sex marriage.
I would disagree with you use of the word 'owed'. Marriage is not something that is owed per-say to heterosexual people, because there are many cases, whether on legal or moral reasons - basically any man cannot just marry any woman.
Secondly, one must acknowledge the fundamental difference between the nature of a same-sex relationship vs. a heterosexual relationship. The logic that they are the same, and therefore owed the same rights, kind of ignores the differences, one biologically differences between men and women, two the former cannot not naturally lead to the birth of children (without use of intervention of a third party), while the second does. The reason why society sees no difference is because of advances in other areas that favour against child bearing
(e.g. the idea of a business women being more useful to society apparently then being a mother raising children, discouraging women from getting married or if they do get married, from bearing children), and thirdly, gender differences (if we are making the distinction), the way a biological male thinks is different to the way a biological female thinks, their brain structures are slightly different).
I agree that marriage is not something universally agreed on, as it is evident by the differing views on its debate. But what is the essence and basis for marriage really? That is the fundamental question. if it is as Christians propose, the basis of marriage being a lifelong commitment of a complementarian relationship (including the bringing about of children), then by nature, homosexual relationships not matter how sincere, cannot fulfil that, and therefore cannot be called a marriage. (and thereby consequently should not be called such in legal terms). In fact, the debate in Australia is fundamentally a definition debate about marriage.
All that talk about rights, well of course if you have a broader or looser definition of marriage, and gender, and that men and women should be equal every way, then of course you will say a homosexual relationship is no difference to heterosexual one. The whole same sex marriage debates comes from the same movement that brought us radical feminism in a way.
So in the end, the reason why we oppose SSM, is that marriage is grounded in the complementary principle of a man with a woman; something that is for the good for society, for the good of children, and for the good of women.
I agree with your argument on law being used as means to "discriminate" at risk individuals, and the example listed.
I don't really have much knowledge concerning the implications of same sex marriage in terms of its impacts on the construct of family, so I won't comment on that.
Again, I cannot comment much on the details either. I'm more appealing to what is commonly understood, but I have read some of the psychology stuff around it, but again that's not really my expertise.