Yes, we can.

[Alex]

No on the IRS. I don't see any reason why two married people living in different houses should get different tax consideration than two unmarried people living together.

No on the contentious divorce. If the government isn't defining marriage then there is nothing for government to dissolve. Either the people in the "divorce" will never have legally solidified their relationship in which case they are free to walk away however they want or they have legally solidified it in other ways and they can pursue remedies through the civil courts.

Irrelevant on child custody and support. Those laws already mostly exist independent of marriage anyway and to the extent they don't, they should regardless of what happens with marriage. It isn't like I get out of supporting my child or lose any legal right to participation simply because I was never married to the mother.