Well go check it out, the license that you grant can be revoked. The only reason this doesnt happen more is that most freedom software has many authors and a c

Well go check it out, the license that you grant can be revoked. The only reason this doesnt happen more is that most freedom software has many authors and a change in license would require consent from them all. But a really nasty person could still decide to rip his copyrighted pieces out of any previous version thus crippling the whole project. But nobody is an asshole like that, but legally the possibility exists.