It's hard to get to the meat of your arguments because they are riddled with logical fallacies. You seem to be trying to wedge as many in as possible.
Regarding your itemized "summary":
1. You seem to forget that YOU are the one asserting the validity of YOUR comparison between HFT and bitcoins. So, the onus is on YOU to prove it. So far, you have failed. Beyond that, I simply stated that I am no bitcoin expert. But, I believe my summary of bitcoins was sufficient and relevant to draw the distinction. If it wasn't, then you should have explained how I missed the mark and why that miss is relevant to your argument.
2. Are you kidding? So the fact that there are people who have cancer but not yet died from it proves that cancer is good for you? I mean your argument here is literally: HFT exists; there are stocks that are doing well; therefore HFT cannot be harmful. Wow.
3. You introduced the straw man. Don't blame me for noticing. As for much of the rest of the stuff you wrote, I never said it.
Ditto the Mark Cuban stuff. Not sure why you invoke him or the question of understanding the market for that matter. Likewise with the 100% market efficiency comment. I never referred to any of that. How many straw men are we up to now?
You do a really good job of arguing with yourself, but you fail to address my original point. Your talk about bid/ask spreads does at least address market mechanisms, but even if we were to accept all of the great wonders that HFT does for spreads at face value, that is a far cry from rebutting my OP, as spreads are but a small part of the picture. In fact, it is so insignificant to this discussion, let's call that one a red herring.
I also noticed that you left my example in the extreme completely untouched. Wise decision.
In any event, you joke about my not offering evidence, but the irony is that much of this actually is self-evident. For instance, who do you think is sitting on the other side of the trade when HFTs profit? I won't ask you to buy my trademarked brand of common sense this time though: http://www.nytimes.com/2012/12/04/business/high-speed-trades...
That's an actual study, not an Amazon review from some random "day trader". BTW, it is slightly hilarious that you referred to that review as "evidence".