I think to understand most HFT market makers you have to understand how the markets pay.<p>Most work on a maker taker model.  Which means the trader who initiates the trade pays a small fee and the trader who is the passive side, the one who had their order in the market already, gets paid a small fee. as a side note there are inverted markets but lets leave those aside for now.<p>This means to get paid you want to be at the top of the book, which means you are the first order to get filled when someone crosses the spread to get their order filled.  the way priority is determined is first by price and second by time.  So you have a very vested interest in being the first to cancel and move your order to the newest price level.<p>Exchanges have tried introducing some order types to alleviate this constant send&#x2F;cancel routine such as the order type &quot;Hide not Slide&quot; but people tend to get upset at these order types.<p>Once you understand this, you start to realize that almost all HFT firms aren&#x27;t quote stuffing, they are just jockeying for position at the top  of the order book.<p>I&#x27;ve never really understood quote stuffing, the same firm that quote stuffs still has to deal with those quotes coming back, its not like the market data has a flag saying ignore this quote change as its caused by your own quote stuffing.<p>The way most markets are setup is that quotes come from gateways and multiple symbols all share a single gateway, usually assigned alphabetically, so A-F tickers all share the same gateway.  This means that if someone is actually slowing down market data for say AAPL then they are also slowing down quotes for AMZN as well but again, the same firm that is quote stuffing also has to deal with their own mess so I can&#x27;t see the benefit.<p>Another comment complains that HFT firms don&#x27;t like the fragmented market.  That is true to a point, but keep in mind most HFT strategies only work due to the fragmented markets and RegNMS.  So while they may not like 11 venues, they certainly want atleast 3 or 4, and many  of hte top HFT firms run their own dark pools, adding to the problem:)<p>As far as Hillary Clinton introducing legislation to curb HFT trading, she was the senator for New York.  I&#x27;m dubious of her coming down hard on Wall Street.