The tweaks have a purpose, though. Generally when we talk about taxes we are thinking about funding the core services that everyone (yes, everyone) agrees on. B

The tweaks have a purpose, though. Generally when we talk about taxes we are thinking about funding the core services that everyone (yes, everyone) agrees on. But the system is used to do two other semi-related things. One is to reward one's constituency with tax breaks and the other is to install direct or indirect penalties on behavior. Taxes-as-funding can be simple. Those are revenue type conversations that also happen in every business on earth. Taxes-as-behavior-modification is where things get truly convoluted because you have different groups tacking on their own dis/incentives (so the thing as a whole will lack cohesion) and the number of edge cases simply explodes. "We want A, but not B, but A->B so we'll add a new rule, but that..."