[theorique]

Put a 24 hour hold after a stock transaction is held before you can sell and you just killed 99% of HFTing.

Not just HFT - you just killed some significant fraction of all forms of trading. Bought something and it's declining? Oops, too bad, you're locked in - better wait 24h. The arbitrary phase shift of transactions will add massive amounts of complexity and create a new system to be gamed.

Edit: Also, regarding "skin in the game" - the recent $440M Knight fiasco shows that firms participating in all forms of HFT are exposed to real financial risk. They definitely have some skin in the game.