There is the argument that much harsher punishments for less serious crimes make people think "we'll, I'm screwed now, might as well go all in" and instead of driving 30 kph over the limit, they end up 80 kph over the limit, and crashing. Or someone who has assaulted someone figuring that if they get identified, they'll be put away for ever, and so they go on to kill their victim in the hope of getting away with it altogether.
As usual, the argument is far more nuanced than most people can be bothered thinking about.