There is plenty of criminology research, including research focussed on long term use of surveillance cameras in London, that supports what you've said.
- Many perpetrators are committing crimes with alcohol and drug impairments, mental disabilities, and as "crimes of passion". You could point 1000 cameras at the scene of the crime and many perpetrators are not going to notice nor care about the cameras. Unfortunately for surveillance camera proponents it's typically the crimes most warranting prevention and investigation (e.g. crimes such as assault) that are impacted least by surveillance cameras. Surveillance cameras instead have been found to have some deterrent effect on minor property crimes (e.g. theft of bicycles or cars) but whether the state is going to invest the resources into investigating and convicting someone who stole a <$1000 bicycle is questionable especially when insurance exists and the onus can then be placed back on property owners to do more to secure their property from thieves.
- Perpetrators were being convicted without use of surveillance cameras and can continue to be convicted without use of surveillance cameras. There may be some argument that surveillance cameras help reduce the cost of getting a conviction (e.g. less evidence needing to be captured?) but not much support to the idea that conviction rates are higher. Quite often the courts, corrections system, government (for funding), etc will push back for a number of reasons--lack of funding for courts to hear minor cases, lack of funding for correction systems, correction systems being found in their current state of funding to have adverse impacts on future criminality, etc.
- The cost-benefit of operating surveillance cameras versus the cost-benefit of spending on other areas of policing (or just public spending in areas such as education and welfare) is hotly debated. Total cost of ownership for each surveillance camera is typically a lot more than people may expect, particularly due to the labour cost of reviewing and processing stored surveillance camera footage. There are of course all the other obvious costs too--camera equipment every X years, poles, cabinets, electricity conduit installation, data cable conduit installation, wireless repeater installation including leases, backhaul data costs, data centre hosting costs, labour costs for support/operations staff--none of this is cheap. What if this same funding was instead invested in other programs--would there also be reduced crime levels some years in the future?
[1] https://en.wikipedia.org/wiki/Closed-circuit_television#Crim...
I think you're missing the real intent of their proposal, which is not to give them due process and release them. Their other comments make it very clear they just want certain people to be gone from their local spaces.