If they want contributions back, they are welcome to add a clause to the BSD license or use the GPL (or write their own), but they choose the BSD license in its current form and then get upset when someone stays within compliance of the license while doing something they don't like.
The costs inherent in legally enforcing positive social behavior are exactly why BSD authors don't choose the GPL to begin with, and instead attempt to achieve their goals through social rather than legal means.
Objecting to GPLers re-licensing their forks of BSD projects is part of that social mechanism, and is entirely consistent with the choice of license.
The costs inherent in legally enforcing positive social behavior are exactly why BSD authors don't choose the GPL to begin with, and instead attempt to achieve their goals through social rather than legal means.
Objecting to GPLers re-licensing their forks of BSD projects is part of that social mechanism, and is entirely consistent with the choice of license.