I dont think we have never seen an united front against mutants in the MU. Krakoa right now is having problems with a bunch of losers with depower armors and yellowjacket. YELLOWJACKET ! an Ant-man villian. Do you call that an united front? If all the humanity was on board to use the heavy hitters , well they would be doomed.
Not just now. After House of M they could have been easily wiped from the face of Earth or in the M-Pox crisis (Without Strange and and Wanda the school couldnt have been moved to limbo and Rogue would have died from the M-Pox) Is a bit tiresome hear the X-men blame the avengers about all their problems , specially when they have to take care of all the world not only 1% of th world.