No glitches are NOT bad. Have you ever read Sirlins piece on bannable things. He makes a very specific post that glitches in games don't make them bad, and I think uses puzzle fighter as an example. Game Designers intent is not what makes a game good, because that assumes that all game designers are capable of making great games(and more so did not mess up this particular time). Something being a good test of skill or fundamental strategies of value (things like reading your opponent, spacing, reacting, control of your character, and game knowledge) are what makes something good. If those elements test those things they are good. Go figure DACUS tests ALL of those things actually (or rather can only be fully utilitzed when the player correctly uses those things).
Smash is LITTERED with things you could call glitches that improved the game play. Smash DI, B reversing (seriously doubt the momentum shift was intended), L canceling and Wave Dashing by some (although I personally hate those things), ledge canceling, glide tossing. WIthout those things Smash would not be what it is, the thing that made people play it for years and years.