GPL only restricts one from being a dick. "Unfair!"

If someone requires other terms, the existence of GPL code in no way restricts them from writing or buying other code that is compatible with whatever terms they require.

Anyone crying about that is only crying that they are not allowed to steal something that is already free.

From an authors perspective, do what you want. Don't use GPL if you don't share the single value it enshrines.

It doesn't make you righter or more rational or the GPL wrong or anything like that, and the desire to rent out access to the use of a secret is the most common and least interesting thing in the world, as is the desire to try to present that as being any sort of principle about freedom instead of the crass food-gathering thing that it is.