You are entirely misinterpreting the Brave engineer's good faith argument. The argument wasn't that billboards somehow pay for roads. You introduced that analogy, and the reply showed where your anology falls apart. The argument was that unlike roads, most websites aren't funded by taxes and won't be for the foreseeable future. The engineer also points out some ways Brave ads are different from billboards: they are opt-in, they are personalized, they give you useful tokens for your attention, etc.
It's impossible to ignore that every major browser is subsidized by either user tracking or OS sales. Even the privacy focused Firefox, which I use and love, is funded almost completely by Google ads.
And lastly, one great thing about Brave is it's completely (besides maybe Widevine, which isn't their fault) FOSS, so you are free to fork it and remove the Brave ads functionality. In fact it's probably not even hard to write a script to do it automatically. But no one has successfully funded large scale browser development while being FOSS and not relying on ads.
Also, I know people who would opt-in, though I wouldn't myself.