&gt; They insert themselves into the transactions<p>Be very clear what you mean when you say this.  Because the vast majority of the time when people talk about HFT, the only way the &quot;insert themselves&quot; into transactions is by acting as the counter party to one side of the transaction.<p>In this context they add a lot of value to the system, they smooth the demand curves in time and take on some of the risks of warehousing supply.