> The stock market provides an efficient medium for the allocation of capital.

Only if P=NP.[1]

Besides

  Efficiency: the ratio of the useful work performed by a machine or in a process to the total energy expended or heat taken in.

This also begs the question: "To efficiently allocate capital (energy) for what goal (work)?"

And it doesn't look like the answer to that is "the betterment of humanity", but to push the bell curve of wealth as far to the left as possible with the longest tail possible, externalities be damned.

The stock market isn't a usefull tool for society like kickstarter, but a wealth extraction mechanism for the wealthiest.

So I'd argue that HFT isn't any more immoral than T.

1: https://arxiv.org/abs/1002.2284