Just because the exploit is illegal in one circumstance and not in another doesn't mean it's not an exploit.
When the exchanges are complicit in the deal - being paid for sending information early to particular parties - it's pretty easy to argue there is a conspiracy to defraud the general public, and so regulators have regularly argued:
I don't understand. Using the multicast quote stream (which costs a few thousand/month) is an "exploit"? Or are traders somehow obligated to ignore the actions of other traders? Perhaps anyone using a computer is obligated to act as an agent for people without a computer, rather than a competitor?
I truly don't understand what you are arguing. Could you please explain the mechanics of what you believe should be illegal?
The article you linked calls it insider trading and not front running. In addition, the issue discussed in the article is about making company information public earlier to a select group of people (which is insider trading). However, most HFT (particularly market makers) do no care about this and rely only market data provided directly from the exchanges. This data is provided fairly to everyone.
When the exchanges are complicit in the deal - being paid for sending information early to particular parties - it's pretty easy to argue there is a conspiracy to defraud the general public, and so regulators have regularly argued:
http://www.gotgoldreport.com/2014/03/why-new-york-ag-wants-c...
I assume that when these practices are finally banned you will change your tune, right?