I'm actually fine with effective rates approaching 100% in higher brackets in real use. Inflation is a sunk-cost. If the investor were instead to put their money under their mattress, they have negative real returns, so effective tax rates of 100% would still incentivize investments to offset inflation.
You are right about the sink cost, but ignoring a very real risk. Taxing capital gains to the point where the investor has negative returns drives capital offshore to places where it will be taxed far less or not at all. It turns honest citizens into tax cheats, and we already have too many of those.
Other than that, I completely agree with you.