Noone ever takes Amendments lightly. But not Amending the Constitution when we should might allow developments injurious to the Republic, that could have been prevented. As general statements, I assume you agree. I also know that your statement: ("Leaving the Constitution unchanged is to everyone's best interest.") is given in the specific instance of marriage law, which in a limited fashion, is currently left to the states. All things being equal, I agree.
But everything is not equal. Limits on the judiciary are governed by the legislative branch. OK, then the state legislatures need to govern and rein in each of their judiciaries. However, a federal Amendment that limits state judiciaries but not state legislatures is in no way anti-democratic, and I think if the super-majorities needed to ratify the FMA are there, so be it. I am in favor of it myself.