To make this more clear to some of you.
The movement for stages like PS2 or GG inside the SWF stage discussion forum is, AFAIK, less of a movement to unban stages X, Y, and Z, but rather to change the way of thinking about stages-something that we ban once we see that there is a real reason to ban them, as opposed to something that we ban to have the least interesting game possible, something resembling street fighter at best.
As to why this concept matters, you really only have to look at what they add, competitively. Let's say we work backwards (everything is banned, stages are unbanned one by one). When I add FD, I have a game where, when I main a character, I have to learn 38 matchups on one stage.
Now we throw Battlefield into the mix. All of a sudden, I still have those 38 matchups, but some of them play drastically differently on battlefield than they do on Final Destination!
Now we really throw everyone for a loop and add Norfair to the mix. Now I still have these 38 matchups, but now I need to not only learn how to play them on Battlefield, Final Destination, and Norfair, but I also have to learn how to play on Norfair at all! Once I've done that, I find that trapping my opponent with the lava if he is inexperienced becomes a very potent strategy, forcing him to learn how to play the stage or to die (imagine it, if you will, like a character matchup-if I run into the ICs and never have played against them before, I won't know that one grab = death until I've already suffered it. If I run into norfair without ever having seen it before, I won't know how to deal with the lava). I also have to, in turn, find ways around this strategy.
Now we add PS2 to the mix. Now I still have the 38 MUs, but not only do I have to know them on these 4 stages, have to know how to play on Norfair, but now I also need to know how to deal with PS2's transformations, know how to take advantage of the changes to the best of my ability, and how to get around things like MK's uair on the air segment. This is a RIDICULOUS amount of things you have to learn to play the game competitively at a high level. In other words: it adds to the competitive merit of the game.
So in short, by adding more stages, we are almost always making the game more competitive by giving it a longer learning curve. If you only have to learn 38 matchups on FD... oh well. If you have to learn 38 matchups on FD, Battlefield, Norfair, RC, Halberd... It's a lot to learn, and a lot more chance for someone to shine who is good at many facets of the game, instead of just one particular part.