Sure, and I happen to agree, I release stuff under (A)GPL for exactly this reason.

I guess the confusion stems from this phrasing:

> If it's MIT, the person who buys it ISN'T allowed to give away more copies for free if the seller doesn't want them to

I assume you meant:

> If it's MIT, a seller is allowed to relicense under a proprietary license and then the buyer isn't allowed to give away copies

I had understood the opposite.