[ubernostrum]

But how could it remain free (as in freedom) if redistribution has strings attached?

This is the problem right here; you used a term without bothering to mention that you're using a very specific definition of that term. In your view "freedom" does not mean maximizing my rights to do things with the software; instead, it involves deliberately limiting my rights in order to force me to pass along (your definition of) "freedom" to others.

There are definitions of freedom, many surprisingly common, which do not include that little quirk, and you'll find that "give up some of your freedom for someone else's sake" is, to many people, like saying "pay higher taxes so someone else can benefit".