Does microwaving destroy nutrients in food?
Anything that breaks down due to heat is going to break down no matter HOW you cook it. Boiling only "destroys" nutrients by leaching them away into the water, which is the same reason that other people say that steaming/microwaving is better.

Thiamine, for example, is highly water soluble, so boiling is out. But it also breaks down at 100C, so you can't really cook it either. Niacin, on the other hand, leeches into water, but it's not heat-sensitive, so you can cook the hell out of it, as long as you don't get it wet. Folate is so fragile you can't leave your leafy greens in the sun without it breaking down (common with acids).

Basically, almost everything is better uncooked, but a lot of things are impossible to eat if you don't cook them enough to break down the cellulose. So eat a balanced diet, and stop worrying about the microwave.