In listening to the debates surrounding Proposition 8 in California and the building of the mosque a couple of blocks from Ground Zero in New York, there seems to be an implicit assumption among folks on both sides of the debate that the Constitutionality of their perspective happens to line up quite nicely with their view of what is right and just and good.
However, this is simply not the case. Just because something is deemed to be permitted by the US Constitution doesn't mean that it is morally right. Similarly, just because something is "obviously" just, doesn't mean that it is Constitutional. In this respect I think it is helpful to recall that slavery was Constitutional prior to the passage of the 13th Amendment.