Comprehension fail

By definition, 100% of lawbreakers break the law - so the 'make murder legal then' point is idiotic. The point being made in respect of mobile phone use when driving is that a substantial proportion, possibly a majority, of all drivers do this. Having laws that most citizens break is considered a bad idea since it tends to bring the law into disrepute.

There's a stronger argument to be made as regards speed limits. I'd imagine there are very few drivers who can honestly claim never to have driven at 31 in a 30-limit. But the real purpose of the speed limit is to stop people driving at 50 through a 30-limit, which very few drivers do.