Bats is a full fledged exchange now, as is direct edge. Liquidnet is still an ECN, where large institutional traders try to trade in large blocks. I meant CBOE and their CBSX, not CME, my mistake- they are still an options/futures venue. I am not sure what you mean by a retail market? When you put in a buy order with e-trade, they hit these same markets- they have to hit all the "protected markets" as defined by reg nms (any market that officially registers as an exchange).
The SEC is fairly quick with the paperwork actually, and it did not cost that much, at least not to be an ECN. The direct filing fees were somewhere in the 4 figures, how much exactly, I am not sure- I was on the technology side. Total costs were much higher, as we had to provide paperwork and evidence that we met their requirements.
Market making as a profession, where there is a guy that stands in a pit and makes markets, is pretty much dead. Its all electronic, and the electronic "paper trail" pretty much ensures that you won't get front run. Your buddy today wouldn't just send an order for $32k to the floor, he would send it to one of my algo engines, where we would spray it out and take the top of book at every trading venue we connect to until he had it filled, or sent it to a different type of algo engine that would spread the order out over a time period he controlled and sliced and diced it in the market until he got his fill- the whole point of which is to reduce market impact. HFT guys might be sniping 100 shares here and there to make a fraction of a cent on a strategy that has nothing to do with yours- they might have actually moved the market in your favor.
During market panics, the good old fashioned kind driven by fear- the difference between microseconds and 2 hours is gigantic don't you think? Imagine it being 2007, and saying what difference does it make if my house sells in 2 days or 2 years? Good old fashioned market panics are somewhat tempered by HFT btw- most of these strategies are based on mean reversion, so if prices get too out of whack with what is typical, the algos buy and sell to bring everything back in line. Of course those algos bring on new types of craziness, but no one was looking to outlaw people from trading before computers came on the scene.