Probably most in that position never ever even consider it at all. I have often thought that the institution of marriage as it is often practiced today is at least partly in such a state because Catholics just accepted many of the instances where the civil take on it departs from actual marriage. Maybe if a stand would have been made on things like this by folks who treat it differently than the state there would be more precedent for the broader culture to reject things like ‘gay marriage’ now.
Freegards
You can hardly OK contraceptive marriage, divorce and second (adulterous) marriage, obvious not-committed-for-life marriage (e.g. with pre-nups) and then accuse the GAYS of redefining marriage.
The gays are simply stepping into something which the "straights" (liberals and conservtives, secularists and "religious" of all denominations) have already re-defined beyond all recognition.
WE de-constructed marriage. The gays just said, "Hey, we can get into that."