Two things, actually.
First, none of the three are proper subjects for the federal government under the Constitution. Neither domestic relations law governing marriage, nor health care, nor tort law are matters enumerated for the federal government.
Powerful groups on the liberal or conservative side ignore the limits of the Constitution in order to change that in each case. Gay marriage advocates want the federal judiciary or Congress to override state marriage laws.
President Obama and Democrats forced the individual insurance mandate down our throats with the assistance of the AMA and health care-related associations, and those same health care associations have enlisted Congressional Republican leaders in an effort to override state tort law by effectively immunizing them from medical malpractice lawsuits.
In each case, the advocates ignore centuries of established common law precedent and the clear writings of the Founding Fathers. Congressional Republican leaders oppose gay marriage and Obamacare, but their own hypocritical campaign for federal limits on medmal lawsuits invites Democrats and gay marriage advocates to do so for their causes.
The second similarity is that truly principled constitutional conservatives and Tea Party-side legal experts recognize that Uncle Sam has no business overriding states' rights in any of these cases.
Ken Cuccinelli, Attorney General of Virginia, gave an interview last August in which he stressed the importance of maintaining a consistent defense of the state' authority over marriage. "The Supreme Court ruled that marriage is not a subject that the federal government can exercise jurisdiction over," he said. "Including the courts."
"Frankly, I think it is worth some consideration for the things that aren't reached by the federal constitution to just leave it to each state... As between the two options, I certainly prefer the states deciding these constitutional questions and I don't mean just the one you raised. I mean all the ones that fall in that gray area of whether or not the federal government can do it. If it is a gray area, the federal government shouldn't be able to do it."
Cuccinelli became nationally known for his lawsuit against Obamacare, and he took a forceful stand against federal tort reform last fall in an opinion piece and during the Republican Presidential debates.
I'm thankful that my state's Attorney General understands the proper role for federal power and won't hesitate to defend our rights in court.
Other Republicans have compromised their self-proclaimed "Constitutional conservative" status by pushing to federalize tort law and calling for a constitutional amendment banning gay marriage, even though most states have already done so through election referenda.
Rep. Michele Bachmann exposed her hypocrisy over states' rights, simultaneously slamming Obamacare while pushing federal medmal limits.
Cuccinelli nailed her on it during a debate, but Rep. Bachmann remains an undaunted flip-flopper on states' rights.
Rick Perry, Rick Santorum, and Rep. Bachmann failed to grasp their own inconsistencies on these issues during the campaign, while Ron Paul remained a true constitutional conservative on all three issues.
A constitutional amendment to define marriage isn't necessary unless the federal judiciary overrsteps the limits of its authority and crushes states' authority over marriage law.
Overstepping constitutional limits brings political consequences. Voters no longer trust Democrats who insist that they can force us to buy a commercial product such as private health insurance, and we want the Supreme Court to declare the mandate unconstitutional.
But Americans also won't easily trust Republicans who proclaim their allegiance to the Constitution and the Bill of Rights, then sell out to business interests in the heat of political campaigns by pushing for tort reform.
Gay marriage advocates who try to shove their interpretation of the Constitution down our throats also face a real backlash from a public sick of excessive federal power in areas reserved for local control.
UPDATE, May 19: I discussed this in a radio interview on the "What's Up" radio program, hosted by Terry Lowry and broadcast on Sirius Satellite Radio and on 12 FM radio stations. You can listen to Segment 1 here and to Segment 2 here.