You do pay a fee for mail service. While USPS is not directly funded by taxes, it is funded by the Federal Government. Our taxes are responsible for financing the government's initiatives.

The problem is that the cost to bulk mail (at least 200 pieces) is merely $0.19 per piece. If you want to DOS an entire zip code regardless, EDDM is actually cheaper (per piece) at $0.187. USPS is getting that money. You would need to pay a fee higher than $0.19 per piece of junk mail that you receive for USPS to just break even.