Imo, if Sableye should be banned for anything, it should be for the way in which it can completely dismantle stall teams. The meta without Sableye is great because both Stall and Offense are equally viable. I think letting Sableye roam free would have a very negative effect on this balance, making stall much less viable and encouraging the use of heavily offensive teams that don't get messed up by Sableye.
Look at Adrian Marin's list of stall pokemon earlier in the thread. Sableye beats every single one of them 1v1, with the possible exception of Clefable. Prankster Taunt messes with all of them sans Slowking and Exploud. But the best Exploud can do is 3HKO with Boomburst if it's Scrappy, and if it isn't, Surf is an 8HKO at best.
252+ SpA Exploud Boomburst vs. 252 HP / 252+ SpD Sableye: 151-178 (37.3 - 44%) -- 100% chance to 3HKO after Leftovers recovery
252+ SpA Exploud Surf vs. 252 HP / 252+ SpD Sableye: 65-77 (16 - 19%) -- possible 8HKO after Leftovers recovery
Slowking can't do any better:
0 SpA Slowking Scald vs. 252 HP / 252+ SpD Sableye: 63-75 (15.5 - 18.5%) -- possible 8HKO after Leftovers recovery
Even if it gets a burn, Slowking can't break Sableye, and the best it can do is dragon tail it away.
Sableye can't touch Magic Guard Clefable, but Moonblast still only 3HKO's.
4 SpA Clefable Moonblast vs. 252 HP / 252+ SpD Sableye: 150-176 (37.1 - 43.5%) -- 99.2% chance to 3HKO after Leftovers recovery
If Clefable has Unaware, then it loses just like everything else.
Another popular stall pokemon is Ho-oh, which is immune to W-o-W, can easily burn Sableye with Sacred Fire, and actually 2HKO's Sableye with Brave Bird + burn damage. However, Pokemon like Tangrowth, Alomomola, and Corsola - all popular stall pokemon - all lose easily to Sableye. If Sableye is running Seismic Toss + WoW as its main damage method, Chandelure walls it, but has to watch out for Foul Play or Knock Off. To deal with Sableye, stall teams have to have an offensive Pokemon or two, at which point they are no longer full stall, and have become some form of semi-stall. All Sableye needs is a cleric and it can easily destroy a stall team, and this is why I feel it is unbalanced and needs to be banned.