There's no functional difference between making sure you're under 50 and making sure you're under 55. It's just a number.
I prefer a sensible attitude to speeding, with a bit of human judgement (i.e. recognise that doing 33mph past a school at kicking out time is worse than doing 90mph on the motorway at 2 in the morning), but the fact is that speed cameras - as stupid, offensive and personally annoying as I find them - do save lives. Speeding isn't the biggest factor, but it's an easy one to police, and policing it does help.
I prefer a sensible attitude to speeding, with a bit of human judgement (i.e. recognise that doing 33mph past a school at kicking out time is worse than doing 90mph on the motorway at 2 in the morning), but the fact is that speed cameras - as stupid, offensive and personally annoying as I find them - do save lives. Speeding isn't the biggest factor, but it's an easy one to police, and policing it does help.