Role reversals in Marvel comics?
 

Have there been any major story arcs where all the heroes and villains switched sides?

If you mean they all started off as heroes and then became villains (or vice versa), then nothing comes to mind. I'm not saying no one has done it yet - I just can't recall any offhand.

There have been several times where the hero/villain roles are reversed, but they started off like that rather than evolving into it. And they usually take place in alternate realities/dimensions (What If?, Elsewords, etc). DC's Crime Syndicate of America is a great example of this.

I'm talking about something similar to the "What If" comics...sort of a mirror image of Earth-616. Example...the X-Men are a group of mutant supremacists and it's up to Magneto to simultaneously oppose their radical methods and prove to the world that mutants can be good.

I can't think of anything in-continuity for Marvel along those lines. The "What If...?" series is about as close as Marvel gets to something like that.

I wouldn't say "ALL" but in Superior Spider-Man obviously Doc Ock has taken over spiedy's body, and now if the cover is to be believed he and the sinister 6 are taking on Venom (Flash Thompson) So Anti-Hero Spidey, and the sinister 6 (Bad/good?) vs Venom (Good)

Crazy!

http://media.bestlittlesites.com/ima...013006-col.jpg

Stupid is more like it (I personally can't stand that story arc).

And doesn't really fit his request anyway. Plenty of heroes/villains have switched sides individually over the years. I think he was looking more for a "Mirror Mirror"-type of story.