Very well said and logical.
First, of course marriage should be left to the states. Stopping federal courts from intervening is a wonderful idea, but hardly needs an amendment. Stopping state courts is completely outside of the jurisdiction of the federal government. If a state court finds it unconstitutional then the people of that state should change the constitution. To force a state to accept an unconstitutional law defies every principle of federalism.
As for number 2, it is irrelevant that the FMA writes discrimination into the constitution. Every single court challenge on this including the infamous 9th Circus concludes that a state has a compelling and legitimate interest in maintaining traditional marriage for heterosexual couples. As for No. 3, There is no, I repeat NO chance homosexual marriage will ever see the light of day in any state that does not desire it. Massachusetts has the ability to change its constitution, just as does every other state.
Then why this amendment? The president sees himself as weak in terms of his traditional base, and so in spite of the fact that this ludicrous amendment has no chance of success, and it is likely he would never push it by himself, he is doing it merely to placate the radical right. What he doesn't understand is that this pandering isn't going to help his ratings a bit. Good news out of Iraq and movement on the immigration issue are the two things that most intelligent conservatives want.
A tiny homophobic element in his base is driving it, and the rest who support it actually believe the lies being told. Wait until someone tells him that tiny element wants a hell of a lot more than just the marriage ban....
Yes -simple and succinct without moral relative tap dancing...