My impression was that OP was using it rather fuzzily, conflating "poor" and "bad" and "unpleasant to be around" and whatever other notions of "bottom" might be floating in the air, in the service of a general air of contempt toward Those People. I took it to mean wealth when talking about taxes, to mean behaviour when talking about laws and risks to life and property, and to be deliberately ambiguous when talking about public spaces and zoning laws.

In any case, neither the factual veracity of the claims nor their support for whatever policies OP could plausibly have had in mind seem to improve on taking "bottom quintile" to mean specifically "worst-behaved quintile". Notably, "the taxes you pay are to support the bottom quintile" is even more false if it means "the worst people" rather than "the poorest people".

Incidentally, my comment above is currently sitting at -1. I vigorously endorse everyone's right to downvote things they think are bad, but if anyone reading this downvoted my comment because they thought it was wrong rather than because they disliked it politically or because they didn't want to see this sort of argument on HN, I would be interested to know what they think I was incorrect about. (The trouble with downvotes as a signal for improvement for authors is that it's often very unclear what specific problems they are trying to point at.)