Waaaay back in Secret Wars vol 1 in the 80's on the Beyonder's Battleworld, the Avengers joined with the X-men and Magneto and first Magneto and then Wolverine called out Cap for his lack of standing up for mutant rights.
Now decades later, Cap finally realizes they were right.
To be fair, while the Avengers could have done more helping mutants out, the X-Men pretty much considered themselves the final authority in mutant questions. They also had the tendency to isolate themselves from the rest of the superhero community and did things their own way, which quite often wasn't exactly living up the normal superhero standard, especially with Wolverine and later Psylocke involved. Don't get me started on the 90ties, when Cable and Bishop joined with their 'huge' guns.
They never asked for help or assistence in the first place.