I don't see why we couldn't put a time delay in. Something like this: when you commit to a trade, the actual trade delayed for some N minutes, where N is a randomly-chosen value from some distribution. Wouldn't this eliminate the incentive to do HFT?
No, it would affect everyone - that's why it's so bad. HFT traders would just adjust their minimum spreads and continue on their merry way. Sanders' FTT doesn't attack the mechanisms of HFT, it attacks the markets as a whole - HFT would suffer, but so would everyone else. If you want to hit HFT specifically you need to hit the HFT-specific behaviors - either add a per-message charge (like Canada did) or add a tax to cancelled orders.
I understand that a trade tax would affect everyone, but for someone like me who makes maybe a handful of trades per month it wouldn't really do that much to dissuade me from making those trades. I also don't particularly care one way or the other what happens with HFT, I was just mentioning this as a thing people are thinking about.
My big concern with the transaction tax is how it applies to indexed funds/etfs. Those trade all the time so the price impact can be significant for those. Further, depending on implementation, you could easily get taxed multiple times for that as there is a transaction to get in/out of the index, and the internal index transactions.
