I am a frequent cyclist in the area (I commute to work 3 days a week on my bike) I do not like the LTNS as they have created stationary traffic on East Dulwich Grove which one has to navigate. I then turn down Carlton Ave to the Junction with the lights. This junction now feels very unsafe - the lack of cars means that there is a free for all - the normal rules of the road don't apply. Lots of cyclists ignoring the lights completely, whilst children on bikes/scooters/scateboards are all over the show. Plus of course those cargo bikes jumping the lights)I do, of course, slow down, (and actually obey the cycle lights) but one never knows whats going to happen.
The south circular is usually stationary (exascerbated by the thames water works) but again, I can use the shared space cycle paths but the pollution is just not good.
For me the ultimate negative is the affect on public transport... esp any buses using the south circular - such as the P13 which serves alot of the schools in west dulwich.
I think alot of people are very keen on active travel anyway - take away the traffic jam LTNs and I suspect all the cycle users will continue to increase.