It's probably not right to classify all HFT as unscrupulous. However, consider the kind of algorithm that picks up when you're looking for a big amount of stock X, and then proceeds to race you to the other exchanges in an effort to buy from under you; it's pretty hard to justify that as anything other than predatory.

Making money from speculation (i.e. investing) is one thing, but gaming the system for profit is something else entirely, and something that quite inarguably does not add value.