Here is an interesting paper that shows how large space systems might cause so much ozone loss that a few decades down the road rocket launches could be regulated. That is to say - limited or capped. That paper is not definitive in any sense but that is the point. There are factors of 10 uncertainty in:
1. How much global ozone loss rockets actually cause - especially liquids
2. How much ozone loss would be "too much"?
As the Iridium - Kosmos collision showed it is most unwise to allow multiple factors of ten to run around your space policy and space ops spreadsheets and white boards. Before that collision, certain "Cassandras" were hinting that such a collision was likely to happen in the next few years.
Ross et al. (2009) play the same hand. There are factors of ten running around the science and policy that will cause a collision at some point if ignored.