[llukas]

They referred to HFT only - how does it contribute to "success" of modern economies?

It just sucks out value due to stock market implementation.

[__d]

That argument can apply to any improvement in efficiency of a process.

Admittedly any contribution of HFT to economic success (other than that of the traders themselves, of course) is probably fairly marginal, but more efficient markets are probably a good thing.