Technically a microwave is also a metal detector, amirite?

A violent metal detector

The whole metal in microwave thing is a bit exaggerated. While it's true you shouldn't put bare metal into the microwave it probably won't cause a big explosion or anything, maybe just make your microwave inoperable but that is because the reflecting of the microwaves which can be done with many other materials. And many things that are supposed to go into a microwave oven have a foil lining or similar over the food to trap heat, hot pockets among them i believe.

Not really. Stick a piece of metal into something and nothing happens. Metal needs to actually be exposed to start reflecting stuff. A microwave cannot detect hidden metals. It can tell you if something is metal if you stick it in and nuke it, but you probably could have just done a visual inspection in such situation.

Not really. Smooth metal objects won't throw sparks a lot of times. Metal doesn't absorb microwaves, so they could be reflected back to and damage integral parts of the microwave oven.

Untrue. Metal only causes issues if there are very thin parts of metal (like foil) or positions where there's a shorter path between two points through a spark than within the metal. If you put metal things that don't get too thin, like knives, spoons, or bowls made from a single piece of metal, in a microwave it wouldn't cause any issues - provided you also have something to absorb the energy output of the microwave (this is true even without metal - you should never run a microwave without something water-based to absorb the microwaves).

No