There are strange people that like strange things. Games is about giving control to the player within certain boundaries, so anything that hinders the player's control without giving him the chance to should be left out in any kind of game, it is just not natural. Having items and pokeballs does not make Smash random because the player can still react against all of that with skill and prediction. Tripping does, because it's out of your control. Also tripping is horrible from a standpoint design since it favors air characters and hurts those who have to run towards the enemy.
Inducing tripping with bananas, attacks and stage hazards it's okay though.
I don't see why casual or party game is equal to bad gameplay. People argue that Smash is not competitive, and I myself am not (I was when I had people to play with), but I enjoy good, tight and responsive controls with free and organic movement with many possibilites like the ones you find in New Mario Bros. Wii or Super Metroid. That is one of the reasons that I still play Melee nowadays, most of the time alone.