There is nothing fun about sitting in traffic on your commute to/from work, and neither there is much fun in doing long-distance driving in a straight line on highway for hours on end (regardless of the horsepower). That's what autonomous driving is for imo.

There is a lot of fun in driving a high-hp car on track or offroad or in some not-much-populated area or in plenty of other scenarios. That's where using autonomous driving mode would feel preposterous to me.

How much fun is it actually to drive around doing daily errands or commuting?

Personally, I look at the 40,000 people killed each year in traffic crashes in the US, and I think, the sooner we all stop driving (on public roads) the better.

You make a good argument in favor of not allowing 680hp light vehicles on public roads.