I think you have it backwards. This would be a great discussion over a bottle of scotch some evening.
The court can overturn Roe v Wade because it is not a privacy issue, as it previously ruled. At the time Roe was decided there were states poised to pass laws in favor of abortion and no doubt some states would still approve the procedure. Since the US Constitution guarantees “life and liberty” this presents a unique situation/argument. Still, this only affects citizens in each state individually.
On the other hand, because states are required to support other states laws, a gay marriage would cause major problems in a state that had laws against the practice. So, this would certainly be a federal issue.
I can see (see, not necessarily agree with) both sides, which is why this is such a great discussion. If you have read what Justice Scalia has to say on this issue, you would see the logic originalist justices would use. I believe four on the court would overturn Roe v Wade if a case comes up, all logically and constitutionally based. On the gay marriage issue, the conservative justices seem to agree there as well, that without a national law individual states would be required to recognize homosexual marriages.
Scientists try to build a better 'womb' for IVF (Boston Globe -
So instead of getting an abortion it may be possible to "decant" the baby into an artificial womb someday and not kill it. But then we have an entirely new ethical delima: who's going to pay for it all? The state?
I think the reemergence of eugenics as a cause for abortion (aborting because of the wrong sex or inconvenient genetic anomolies such as bad vision) may change a lot of the emotional content of the debate. The first inklings of that have come up surrounding the possibility of there being a "homosexual gene" and the logical consequences that finding that out in routine pre-natal testing could be. There already is a big problem in China with the aborting of female babies in preference for males causing a skewing of the population such that there could be a collapse in their population from lack of child bearing age women.
It may be time to read Huxley again.