So if someone wanted to marry a duck, what would be so terrible.

Seriously; I'm not trying to be facetious here.

Who would care, or why would anyone care?

Because the duck would be on his or hers spouse's health plan at work?
Because the duck would inherit all the spouse's assets of the spouse if the spouse dies before the duck does? (People leave money to their pets all the time).

As far as the "people who want what they want when they want it" having "no other concerns", well, that's very true, but it applies to all people who feel very strongly one way or another about any issue, not just the proponents of same-sex marriage.

I will say, though, that it might be worth the price of admission to see the marriage consumated.

Which reminds me: There are still some ridiculous sodomy laws on the books, which, in some cases I'm sure, make it against the law to have sex with animals other than humans. I'm sure you know that in one state (Texas was it?) laws against oral and anal sex were recently repealed. Why should anyone care about that? (Hmmm, maybe a subject for a new thread....).

It's all part of being perched atop the slippery slope, ready to start sliding. First we'll ban same-sex marriage. And I'm sure that those who oppose same-sex marriage also oppose same-sex sexual relations, so they can go to work on banning that next. And I bet the same people deep down inside oppose sexual relations between members of different races, so that will be the next to go.

Anyway, to go in a slightly different direction: I'm not sure, but I think you kinda begged my question up there...

"Do you really think that this is the single most important issue that Americans face today?"

And the original question, "Do we really need a constitutional amendment for all this?"