Wolverine was a long-time X-Men member and an Avenger. Beast is a Secret Avenger and an X-Men all the way from the First Class. Storm is a recent addition to the Avengers.
Now with all this infighting going on between mutants and Avengers, should an X-Man (current or former) be allowed anywhere near an Avenger team? Maybe if they left a team many years ago that could be an exception, but for characters that flip flop teams, where would you stand?
I'd say no X-Men in the Avengers teams, or else quit one team to join the other.