Yes it would appear as though the sky is falling. Surely this is the end of WoW, as foretold by the ancient prophecies.
After leveling a few dozen characters to various expansion level caps over the years, I can safely say that I see nothing wrong with the potential feature of selling characters. Leveling is not part of the game at level cap. Either you want to level, in which case you level, or you want to play level-cap content, in which case your only option is currently to first invest X hours leveling. Even if you've done it 20 times already.
I think it would be fair to add a constraint that players must actually level a character to level X before they can purchase characters at level X. Could take it or leave it though.
For the fuck's sake, it's a video game.