You can't ban a character by the way. And for your information Dedede and Olimar throw MINIONS not items. They can't be picked up. Also, Olimar has a minion/Ice Climber-esque thing going on. He can control pikmin to an extent, but they also have their own moves and he uses them for attack as well. Very controversial, but pikmin are essential to Olimar's moves and without them he's stuck. So the answer is no, they don't have a special random factor they are being controlled and are avoidable. They don't add any sort of luck to gameplay either.
Items aren't turned off simply for the sake of being turned off. They were mainly turned off because of exploding containers.