Expect a new class of companies to spring up overnight that are dedicated to bundling transactions to avoid this new tax. For instance, I could make a single transaction to my broker that covered all of my expected expenditures for the month, and that broker would then disburse it to my payees, bundling it with funds from other payers to avoid the tax on the other end.

I am strongly in favor of a tax on all stock market transactions, though—anything to deter HFT, which IMHO has little societal benefit while externalizing a ton of risk.