It's an interesting suggestion, this of making more-stringent divorce laws a condition for gay marriage. But who, exactly, would be doing the trading? I could see, perhaps, if the Andrew Sullivans of the country came forward and declared that they would throw their support behind a new marriage regime that granted gays marriage rights while making divorce a more difficult and painful procedure. Hey, throw in an adultery clause, and the equation becomes such that social conservatives (even Catholics, such as myself) might find the scales of evils tipping toward a different "lesser" (away from the current "lesser" of expanding the federal government to cover marriage).
Such an arrangement would (at first glance) make the best of the reality of homosexuality, strengthen marriage among heterosexuals, and completely undermine the certain danger of marriages of convenience. One wonders why Sullivan hasn't made such suggestions rather than shifting into a snide, dismissive tone in order to address the legitimate concerns of those who disagree with him.
I think the naked unlikelihood of enacting adultery laws in the current environment much less with homosexual groups' support points to the reason. Even the most conservative of gay marriage advocates (at least whom I've read) want gay marriage according to a liberalized definition of marriage. Many more want it merely as a new form of entitlement. Still others want it as a means to abolish traditional views of sexual relationships.
The bottom line is that the impetus for the push for gay marriage does not come from a conservative, traditional longing for "a normal family." It may, for a minority of homosexuals, but I suspect that such people would be the sort to give some consideration of the arguments against gay marriage, anyway. Much more of the movement's support comes from those who see it, in some degree, as a further step toward the liberalization of sexual mores.