Sure, let me rectify that and give you an argument.

Driving on a road is about discipline and predictability. Discipline is following the rules, like speed limit, using specific side of the road, using blinkers, stopping on red, etc. That is all necessary, for the driver's behaviour to be predictable to the other road users, both drivers and pedestrians. I'll assume that I don't need to argue that predictability of behaviour in 1 ton caskets going 150km/h is desired?

Given that, refusing to follow belt enforcement rule is a good indicator that the driver decided they can pick and choose which of the rules they want to follow, which makes them undisciplined and suggest to other road users they might be unpredictable.

The law enforcement of that rule intrinsic value lies not in life saving, or monies, or whatever, but in reminding the driver that they need to follow all the rules and behave in a predictable manner.