In fact there was a shitstorm when some licences had "all modifications must be sent upstream" clauses e.g. Plan9's original license had that clause. And then the "tick this box if you don't make nuclear weapons" clause was lambasted in Theo's colourful style [1]. There was a time when OpenBSD were considering moving to the plan9 tool chain - which is now available under both GPL and MIT licensing.

That sad part was, most everyone in the plan9 community agreed with him but had their hands tied by Alacatel/Lucent legal and US law.

[1] https://groups.google.com/forum/?_escaped_fragment_=topic/co...