That seems an exceptional claim. Where I live folks obeyed the speed limit scrupulously where traffic cameras were in use. That has to reduce accidents, as expected?
Hes probably talking about cities shortening yellow lights after they install red light cameras to make more people into "offenders" and cause accidents as a side effect
Any road has a "natural" speed that ~80% of drivers will drive at if not otherwise restricted. If you limit the speed below that, you have a lot of annoyed, frustrated drivers and that is a recipe for more road rage and accidents.
My objection to that is that the "natural" speed may not be taking into account unexpected conditions. For example, it may drive by a school or playground and the speed limit is there because of the danger of children running out. The "natural" speed isn't going to take that into account.
The correct solution here is road engineering so that the natural speed of the road is slower, rather than artificially slowing down traffic via a posted limit. This can be done by adding curves or thinning the road