The X-men have not had the same standards as the JL or the Avengers for years now and they've always been pretty open about letting villains in their ranks. And it's a mutant nation, not an X-men nation.
Also, the JL or the Avengers would have much more support than the X-Men by other nations that could make it easier for them to follow all of their "standards". Besides, current Krakoa is still helping humans.