Just because something supports commerce doesn't mean it should be free. My city (Mountain View, CA) has outlawed plastic bags and requires stores to charge for paper bags...commerce supports that were "free" to the consumer in the past. Yet, for some reason, the city provides TONS of free parking in municipal lots.

Car owners kind of already pay for infrastructure for their vehicles through excise tax, gas tax, and tolls (not really, but at least its something). Why not charge for parking too?