I think most people would like speed limits enforced with some sensible discretion. To give an extreme example, you shouldn't receive a $150 fine for going 1 km/h over the limit. Before photo radar, there were a limited number of police officers to enforce speed limits, so most limits weren't enforced most of the time. Police focused on catching the worst offenders, so going, say, 60 km/h in 50 km/h zone or 110 km/h in a 100 km/h zone was unlikely to be prosecuted. With photo radar thresholds set in many places as low as 3 km/h over the limit, the dynamic is totally different, especially since many speed limits are set comically low, and often times photo radar is placed in locations where the limit decreases for a short distance, or at the bottom of a big hill.

To my mind, the goal of speed limits is to promote road safety by encouraging drivers to proceed at a safe speed that is suitable for road conditions. This is undermined when authorities build an expressway-style road that you'd find rated for 80+ km/h in a traffic engineering handbook and then set a much lower limit and have it enforced with radar traps. This is about collecting revenue, not promoting safety.

I visited Norway, which has photo radar, but also warns you that you're approaching it. The intention seems to be to get you to slow down rather than to stick you with a ticket. It works and I agree with photo radar when it is used this way.