Citations in most states do pay for the cost of law enforcement in particular and other community programs, but that's not a tax or levy, it's a fine used as a financial disincentive to reduce dangerous and illegal behavior. If the cost is $1 a day to have law enforcement, then why not have those who make more frequent use of their services (lawbreakers) may remuneration to partially offset that cost?
Meanwhile, a tax against legalized drug use isn't an unfair burden to the poor, though you're right in that more of the poor use drugs. If my choice is to smoke weed, then the societal cost that comes with additional law enforcement needs, medical needs and financial regulation should be paid by those partaking. The same has been in place for cigarettes and alcohol for decades, and just look at the cost of treatment for illnesses resulting from those substances and you'll see why it's necessary.