My actual opinion on that is that you used to have to go to the square where people were exchanging. People farther distances away simply were not there and had to wait in the newspaper to know what happened with prices. I don’t consider advances in communication to be controversial in that regard. I do think people should be aware of who sees their communications.
Not 'to trade' but to enter the small world of HFT. Many, many industries have capital barriers to entry, I don't really see the big deal. Just as I cannot start an HFT firm, I also cannot start a toy factory or restaurant without sufficient capital. If you actually look at how much money HFT firms earn relative to the finance sector as a whole, they're pretty small fish. They just pay a lot because they have relatively few staff.
Which is to say, to get your brokerage's orders in ahead of a large institutional order.
IOW: Legally-sanitised insider trading.