Economics you have to take into account the magnitude of the forces at play. The extra fuel you use by running catless is pretty insignificant (maybe 5%?), as is the extra gas tax you pay, while the extra poution you're causing is 3000%?
I'm sure an SUV with cats pollutes less than that. I'm not being an environmental nazi or anything, just pointing out the falacies in the reasoning around here.
Besides, if you're not part of the solution you're part of the problem so spare me the "well he's polluting too" bull****.