To those who believe that all markets are rational and efficient, that interventions cause more harm than good, y, an enforced halt seems to be anti-capitalist.
But we are not rational actors. We can get into panics. Panics can stir more panic. Forced breaks allow for the market to reassess data for a few minutes without fear of loss for not acting immediately.
You would think, by the same arguments, that the stock market could always just trade at 15-minute intervals. Why not? But people go crazy when researchers (e.g. Eric Budish at U. Chicago) suggest lowering the frequency to milliseconds, let alone seconds or minutes.
There are different, additional, objections to that. For example, it would make life rather difficult for market makers, which would mean a lot of the liquidity would dry up, which means the spread would widen out, which means trading would be more expensive.
I think there is scope for designing market mechanisms which have the volatility-reduction effects of periodic auctions, but which still allow market makers to hedge. I hope people are working on those.
And how is that a bad thing in and of itself? It would presumably knock out some of the ultra-low-margin HFT but so what? If it would have the effect of turning the stock market into less of a roulette table, with fewer gamblers compared to bona fide investors - isn’t that a good thing?
The circuit breakers also have an important function in relation to the role algorithmic traders play - it allows a bit more time for humans to step in and either switch off or tweak the algorithms if appropriate.
But we are not rational actors. We can get into panics. Panics can stir more panic. Forced breaks allow for the market to reassess data for a few minutes without fear of loss for not acting immediately.