I, uh, don't see a halo. Never have. I see streaks/starbursts, kinda like this quora post [0], except I've seen streetlights like that my whole life (so I don't think it's an eye problem like they suggest). Maybe that influences why I find dark mode easier on the eyes? No blurring, but it's also not sharp enough to cause the starburst.
[0] https://www.quora.com/What-are-those-peripheral-rays-of-ligh...
I think that several other comment threads get closer to the truth of the matter. Your experience will be quite different depending on the dilation of your pupils. Most people have better acuity in bright environments where their eyes behave more like pinhole cameras. Not only does the pinhole have better depth of field than a larger opening, but most people will have more higher order aberrations in the periphery of their cornea. That is why they will see artifacts at night more than in broad daylight.
With a properly balanced viewing environment, you will have the same acuity for light on dark or dark on light, because the ambient lighting should dominate your field of view and set your pupil dilation. The screen should then be bright enough to fit comfortably in the same dynamic range as this environment.
Another factor is screen surfaces, and what people perceive in the dark/black areas. If you use glossy screens, you are more likely to notice distracting and non-uniform reflections in the darker areas. With a matte screen, you will mostly just have reduced dynamic range with the environment affecting the whole screen as a more uniform noise floor. Smudges on touch screens may also affect someone's perception of solid colored screen areas.
White on dark with fuzzy fonts on non hidpi screens is terrible indeed.
It's also great when you're doing image or video editing and need to be able to see full contrast in the dark areas, without being overwhemlmed by bright light surrounding.
But it's objectively far worse if you're reading significant amounts of text, for the simple optical reason that light bleeds inside of lenses, including in your eyes -- that white "pollutes" black but not vice-versa.
Thus with black-on-white text, letterforms stay separate, clear, and legible. Any light spreading simply makes the letterforms appear, say, at 10% brightness instead of 0% brightness. Zero problems with legibility, still plenty of contrast.
But with white-on-black, letterforms glow with blurry edges and connect into each other. Not on the screen, but on your retina. The same way streetlamps at night appear to have a halo. Words take more effort to read. Now granted, if you're 15 years old with perfect vision, it may not be particularly noticeable or objectionable. But the older you get or worse eyesight you have, the more it becomes a big problem.
So dark mode is nice to have, but for most apps going dark-only is objectively bad for accessibility, and legibility generally.