> It's a good way to support a project

I disagree. GPL/Commercial dual licensing is always a game of perverse incentives. Even if you aren't actively crippling the free part of your product you're incentivised to make it difficult enough to work with or otherwise support that companies will be inclined to pay you to do it.

Not necessarily - the GPL is a no-go for some companies regardless of the difference in quality between the free and not free.

Remember that it's not free it's about lawyer approval.

Can you dual license with both GPL and MIT (or other)? Would that make sense?

Maybe, the idea is that a company who wants to use my work can either comply with the GPL and give back that way or financially support the project (and therefore not need to comply).

You could grant them an MIT license, I guess.

FSF isn't vehemently opposed to permissive licenses either (they are merely discouraged), but that is the argument GP decided to bring here.