Arguments against Ridley I've seen in the last 24 hours...
1) Ridley wouldn't be able to do anything--he has no moveset potential.
(Hey! Why don't you come read this thread?)
2) Ridley doesn't have a personality.
(Hey! Why don't you read the manga? Anyway, does personality even matter? Villager?)
3) Ridley is too vicious for Smash Bros.
(Hey! Have you ever played a Zelda game? Ganondorf is no little angel...)
4) Ridley is confirmed to be a stage hazard.
(Hey! Although this is a possibility, it wasn't confirmed, and we can't even be sure it was hinted!)
5) Ridley would just fly around and other characters would have to jump.
(Hey! Same was said about Charizard and Kirby! Besides, Ridley does fight on land, too!)
6) Ridley isn't important enough of a character.
(Hey! He's the main villain of Metroid and appears in pretty much every game!
7) Ridley isn't needed because Metroid doesn't need another rep.
(Hey! Um.... it could actually use one... and besides, it's not about reps, it's about characters.)
8) Ridley can't be in because he was a boss in Brawl.
(Hey! Characters can change roles! Charizard in 64 and Melee, anyone?)
9) Ridley would either be too weak or too strong.
(Hey! That may be the worst argument I've ever heard!)
10) Ridley is too big.
(Nevermind. THAT is the worst argument I've ever heard.)