I think that this is almost universally accepted regardless of people’s personal position on the limit. I personally feel that the dangerous drivers now seem empowered to take risks when driving behind a car doing less than 30 mph.
It is, however, still relatively soon after the speed limit was lowered and I think that we need to see how people adjust over the next few years. Historical road safety measures and more general public safety measures are nearly always deemed unnecessary by sections of the public when they are legislated (e.g. seat belts, seat belts in the rear seats, lower blood alcohol limits when driving, mobile phone use at the wheel, compulsory motorcycle helmets for motorcyclists, public smoking ban). People will complain about a reduction of freedom and/or state that it is not necessary for them personally, but society will generally accept the change and move forward. I believe that there is a plan for busses to be speed limited to local limits on local roads, so this may get people used to driving at 20 mph as, after all, twenty is plenty.