What I wanted to say is that a fundamental purpose of marriage, as well as for the companionship it promotes, is to bind a man and a woman together for life so that their offspring will have the best possible upbringing.
Whose prescription is this? I don't recall when I got married (in 1974, before my 22nd birthday) even discussing children with Mrs G (to whom I am still married). I can't understand your need to be so formulaic about marriage.
Now someone will say what about infertile couples etc. But the principle still stands, in the same way that incest is still incest whether a woman is able to conceive or is infertile.
I think you are doubly wrong here: first on the 'principle' you seem attached to, and second that marriage has some parallel with incest.
So the result of including people of the same sex in the institution of marriage is that there is now no institution which has for all its participants the above principle in view, that is, to tie a child to both of its biological parents.
Nope: the 'institution' as you'd prefer to define simply isn't what you'd like it to be: reality is rather different, just as people are different.
While children are important to those that want or already have them, or would like in future or perhaps they can't or simply don't want to be parents: so children aren't essentially important to everyone who is married. In addition, children grow up to be adults: my three children are aged 35, 32 and 27 but I'm still married to their mother (and hope to be for some time yet). Marriage is what people want it to be, and what they make of it, and it isn't bound by your prescriptive approach.
This can only increase disorder in society, and is why civil partnerships are the best option for people who want the legal rights associated with marriage.
If people want marriage then that is what they should have - it is their decision (if they meet the legal requirements).
