Even if enforcement was "unfair" (let's ignore for a fact that this is not a binary determination and not being able to be perfect isn't an argument for not trying) then everyone having the potential to experience the same hurt from the unfair system is still more fair than a corrupt society where some people can have their lives destroyed by an unfair fine but others can just shrug it off.

I agree it's not a binary thing but you're still viewing it as "an unfair system that is trying its best" vs. "a corrupt society" and my entire point is that is a completely false dichotomy. As Madison said, "enlightened men will not always be at the helm" - you have to design your system in such a way that bad actors are limited in their scope.

Proportional fees "hurt" everyone the same and give the government the discretion to "hurt" whomever they choose via malicious prosecution and selective enforcement. Flat-rate fees at minimal amounts save most people from this corruption. If the difference is between a flat rate penalty that hurts 5% of society if imposed, and a proportional penalty that hurts 100% of society if imposed, how is the first one not objectively better in the nearly certain scenario of a bad actor being in charge at some point in the future?