Bottom line...these are damn fair questions I asked. I'm surprised that no one has yet stepped up with a reasonably rational response.
They are fair questions, which is why they've been answered in this thread multiple times already. The law will continue to be ENFORCED, it will merely not be DEFENDED in court BY THE ADMIN. OTHER INTERESTED PARTIES, including members of congress, CAN DEFEND the law in court in lieu of the DOJ. I have little doubt that "family values" groups will be happy to take up the gauntlet.
From Holder's official statement: " I have informed Members of Congress of this decision, so Members who wish to defend the statute may pursue that option. The Department will also work closely with the courts to ensure that Congress has a full and fair opportunity to participate in pending litigation."
This is not unprecedented, quick googling reveals both the GHWB, Clinton, and W (
http://www.law.com/jsp/article.jsp?id=1202473959808&slreturn=1&hbxlogin=1) DOJs all opted not to defend certain laws. There is no slippery slope so long as this is a relatively rarely used tactic which historically it appears to be. Now, if Obama stops defending a dozen or so laws he doesn't like (not that the standard presidents have employed is anything so mercurial), we can talk about his abdication of executive responsibility.
In any event, the laws in such cases will continue to be enforced until a court rules them unconstitutional, not something judges tend to take lightly. So even if an admin refused to defend a law and no one else did either, the plaintiffs would still have to convince the judges that the law was unconstitutional and that they should take the powerful step of overruling congress. This does not happen often and that's not due to the DOJ putting on impeccable defenses nearly as much as it is due to the deference accorded to legislation.