I agree with Penny about the streamers possibly considered to pollute the water. Maybe even the danger to sea birds getting caught up in the spirals before they have degraded in the water. And paper cuts. Yes, I said papercuts, the kind you get between the thumb and forefinger.
I remember in 1967, I was on a transatlantic cruise. It was tradition in those days to celebrate bon voyage with champagne for everyone and to pop small plastic bottles that would shoot out thin streamers of paper with razor-sharp edges. I remember getting cuts from them.
Now, if you're talking about the tissue paper streamers that are about two inches wide, you may be able to get away with it by dropping them from the portion from the Veranda Deck that overlooks the pool on the Lido Deck. I doubt that it would hurt anyone.
If you asked them they might say no. But, you could take the trojan approach and just "do it but don't get caught."
If you are caught you can play dumb. After all, it's not throwing anything overboard, off the ship.