You're right, that is much more rightfully offensive than just the naming problem.
We have a similar bit of bullshit in British Columbia, where government health insurance is paid through premiums, administered outside of the tax system (which is annoying as hell, and doesn't happen in other Canadian provinces), which are progressive only up until $30k (£18k) annual income, and fixed after that at $900 (£550) /person/year. Which is 3% of $30k/year, but 1% of $100k/year, etc.
... actually laid out like that and looking at the inhuman shitshow in the US, I think I might withdraw my complaint.
But, back to naming because obviously that is what really matters, a regressive tax[0] is still a tax.