But if you use a permissive licence there's no need for anyone to sue anyone at all. Seems a better situation for everyone involved?

If GCC had been more permissively licensed then Apple would not have released its Objective C compiler, which would have been a worse situation for everyone involved (to include Apple: they are simply wrong that a proprietary compiler is better for them).

GPL tries to make the world better, by increasing the free software commons. BSD tries to be neutral, but one should not be neutral in a war of good vs. evil: (cf. Ireland, Spain, Sweden & Switzerland in the Second World War or Sweden during the Cold War).

Isn't that essentially saying "If nothing were illegal there wouldn't be anyone in prison"?

No it's essentially saying if projects like GCC published permissively we could all get along peacefully and wouldn't need to batter each other using the courts.

Except one of the things a "permissive" license allows that the "restrictive" GPLv3 doesn't is locking code behind patents.

Companies like Apple prefer BSD specifically because they want the option of taking someone to court if they want to.

LLVM recently re-licensed to the Apache License (v2) which explicitly provides relevant patent grants on contributed works to consumers of the software.

The issue there is it removes freedoms from your end users. Now there's a multitude of binary distributions of LLVM, and users can't mix and match pieces of them.