Hmm if we all drive at the limit we're more relaxed? More like it turns boring and monotaneous and there is an increased chance of you falling asleep or tuning out and not paying attention to what you're doing! IE doing 40 on the motorway at night because of roadworks even though there aren't any workmen there? Oh and then you spend too much time looking at your speedo making sure you aren't gonna get caught speeding than you do paying attention to whats going on around you.
Anyone who thinks most speed cameras are there for our own safety are very naive imo, they are just revenue gatherers and most accidents aren't even caused by speed.