Here's my arguments for the suspects I support banning:
Damp Rock: This really makes Rain Dance broken in UU, where a truckload of Swift Swimmers are present, and can abuse the Rain to full advantage of the course of eight turns. Without it, Rain Dance teams have less time to sweep efficiently, and the effectiveness of Rain Dance sweepers would then be cut drastically.
Porygon-Z: This thing hits like a truck in UU, easily having the highest base Special Attack. Without a priority fighting type move, a Scarfed fighting type, Registeel (non HP Fighting versions only), or D_A's ChanseyTomb combo, it is extremely difficult to bring down a Nasty Plot Porygon-Z of any kind. With Porygon-Z gone, the centralization of the game around it will be gone as well, and UU will settle down a little bit.
Cresselia: Cresselia can thrive in UU so well because of the lower amount of powerful physical attackers that hit Cresselia for super effective (nothing really hits like Tyranitar or Scizor do back up in OU), and it has decent speed, allowing it to cripple a large majority of the metagame. Cresselia can also easily set up a sweep thanks to its natural bulk (and lower amounts of weather teams, increasing the recovery yield of Moonlight), or can support a team easily through Dual Screens and the signature Lunar Dance.