It would be foolish to say that wall infinites have to be an either/or for banning stages. When considering a stage, you have to take more than one factor into consideration.
Take Shadow Moses for instance. Its banned because of the high ceiling and the dual walls. It has the immortality thing going on (one of the reasons Temple is banned, but not the only one) and matches tend to take too long. But another reason is that the walls are so unavoidable that you can guarantee that a wall infinite is going to happen at least once per match. Remember that one infinite is one stock.
DeDeDe's wall grab is generally more prominent in the mind than a D-Tilt spam because it is easier to set up. I'm all for infinites being legal, provided the stage selection is balanced while keeping them in mind. Deciding the stage list is more or less deciding how the meta-game will unfold. Say, if we allowed both Green Greens and Shadow Moses, amongst many other changes to the current state of affairs, DeDeDe would be an even better character than he appears to be now. The many mid-heavy weight characters couldn't ban both stages for counter-pick, and the match would pretty much be decided before it starts. I'm only picking on DeDeDe because his infinite occurs more often than the others.
Which leads me to my next point: infinites don't happen that often in tournament play. One reason for this is that the stages with walls are rapidly changing, or, don't feature inescapable walls. Rainbow Cruise, Pictochat, and Delfino are all 'morphing' stages. There are walls, but only temporarily. While they are present it is up to the players and their characters to either try for an infinite, if they have one, or to play it safe if they do not have one or are unsure of themselves in executing. But this dilemma will only last for a little while, and the walls will dissapear, and the match can continue on unhindered.
Example: R.O.B. vs DeDeDe on Delfino. The stage gets to the part with the wall. DeDeDe can wall grab R.O.B. until the stage change, and it would be pretty easy to do so. R.O.B. could D-Tilt DeDeDe, but it might not be a good idea to try it, due to the variable levels of difficulty. Result, my R.O.B. would just camp until the stage changes, or stay in a safer location.
Corneria has a wall, but only on one side. Under the fin is certainly a danger zone, but it doesn't decide a match at all. If a heavyweight was versus a DeDeDe on Corneria, they could stay on the top section (safe) or keep De between them and the wall (not so safe.) While there would probably be a lot of camping in this scenario, camping is a play style, while infinites tend to hamper game play. If the DeDeDe is up a stock, and camping the wall, the heavyweight will have to descend into the danger zone, or lose to a time-out. I feel, that this leans more to the Counter-Pick status than the Banned status. (As for banning Corneria itself, more factors need to be taken into consideration. There are occasional hazards, but more importantly really close ceilings and walls.)
Onett is similar to Shadow Moses, in that the walls can present an 'immortality' effect, the hazard has killing potential, there are close side off-screens, and infinites will happen more often than not. Again, walls being present (in regards to infinites) isn't a deciding factor, but one of many.
If I may make a comparison, DeDeDe's chain grab should have a similar effect on walls as it does regarding walk off stages. One reason to ban them is that everyone knows they're gay. Another is that one grab can equal death. Bridge of Eldin, Yoshi's Island (Pipes), and Onett all take that into consideration amongst being too big/small and what not. Not so much Onett.
Castle Seige is allowed for the same reason Defilno, Pictochat, and Rainbow Cruise are allowed. The stage morphs, so the walk-off is avoidable. There are plenty of platforms to camp on until the walk-offs go away. The stage changing animation is a walk-ff itself, but it doesn't really last long enough to get chain grabbed off the stage.
Though I guess we don't want to admit it, keeping one or two techniques in mind while determining what stages to ban should be a valid concern. Its up to us to decide whether DeDeDe becomes a 'broken' character with easy kills on walls/walk-offs, or a still good character without them. Wall infinites are more balanced within themselves, as many people have them and often times both opponents could trap one another. If not, its up to the disadvantaged person to stay safe and play smart for the duration of the match.
A counter-pick stage has to have a certain amount of balance to it. Frigate Orpheon is a great counter-pick stage against tetherers, or characters with bad recoveries. One side of one of the stages has no ledge. This is a pretty big disadvantage, but it is not unbeatable. A smart player would put great priority on staying away from that place. And once the stage flips, it is no longer a worry (until it flips again.) Port Town Aero Dive would be an imbalanced counter pick against those same characters. The main platform has no ledges, so they're pretty screwed once they get knocked off.
Green Greens crosses the line between counter-pick and banned stage. We should take into consideration the inescapable walls when determining What category it belongs in. In regards to the walls, infinites would happen too often and would reduce the quality of gameplay to MvC2 status (yeah I went there.) The stage itself punishes approaching too much and matches tend to be really long, campy, and boring. The blocks can be pretty stupid and can kill characters caught under them, especially ones like Lucario and Olimar. Also, the bombs are a bit too in the way with such a cramped stage. While seperately, many of these aspects sound good for a counter-picking stage, put together I think they manage to tip the scales in favor of being a banned stage. Keep in mind that for a stage to be banned it doesn't have to be 'stupid,' it just has to be imbalanced.
Edrees, sorry for writing so much.
-Preemptive Response-
"You said that camping was good on Corneria but bad on Green Greens."
Only in regards to walls and infinites, Corneria remains balanced enough to warrant counter-pick. I'm not going to touch on the closeness of the stage-off's and the hazards. If both characters have wall infinites, play on. But in the scenario where one character does and the other does not, there is clearly a difference in advantage. The disadvantaged character will have to stay away from that one danger zone. If they are up a stock, they will never have to descend. If they are down a stock and the winner is camping the wall, they will have to descend. The match could go either way, and the outcome is not decided from the start. Also, projectiles can influence the effectiveness of camping the top or bottom of the stage. Camping the turret in front of the stage would be more along the lines of stalling, but simply having neither character approach is more or less accepted. Especially when the person up a stock says to the other "You know I'm not going down there..." and the inevitable approach is forced.
Green Greens punishes both characters for approaching, all the time. Corneria's camping game is influenced by many factors, but Green Greens' is not. You pretty much have to jump in if you want to get a hit in. Characters with projectiles have an advantage on this stage, and that was more or less balanced in melee. But with brawl being such a defensive game it is no longer acceptable. Approaching is already more punishable than it melee, and Green Greens exemplifies this. The two are different games, and should have different ban lists.
Overall, Green Greens is worthy of a ban. In the majority of this post I have been indifferent to Corneria's final resting place upon the list. I have only discussed its wall.
tl;dr
Ban Green Greens. I'm sorry Edrees.