Charles Murray has said somewhere that government support of marriage will do for the institution what government support of religion has done for religion in European countries -- i.e. kill it stone dead.
I agree with this. If marriage needs active government support, the game is up.
Update from Ramesh Ponnuru
My view on this is the same as my view of governmental efforts to help people with children: Maybe it's worthwhile in some circumstances, but it's not nearly as good as ending the government policies that weaken marriage and punish childbearing. Not only that, but the ameliorative proposals are nowhere near the destructive ones in magnitude.