I'm not really sure I understand the fuss over X-Men: First Class' approach to X-Men history or previous story lines. Movies notoriously do NOT slavishly follow their source material

, often they seek to reinterpret.
The movie had no need or desire to follow movie lore, since Wolverine: WTH that was, so deftly crapped over the history established in the previous X-Men movies. Instead it was intended to be a reboot or fresh start to the franchise. It gave us a more daring Charles Xavier, honed Magneto's issues, and defined Mystique's importance in that X-Men's history. First Class didn't take anymore liberties than most super hero movies have done in the past. It also took a rather novel approach by tying it to the likes of swingers & Bond films, to add a new shine.