We propose a nominal tax, of a fraction of 1%, on all financial transactions (sales of stocks, bonds, derivatives, and other financial goods) to encourage market stability and discourage speculation.
Financial speculators, with the aid of computers, currently run millions of high-volume, low-margin transactions, responding to half-cent differences in price in order to earn profits at volume. This creates an environment that encourages recklessness and volatility, promotes the use of computerized group-think which lead to the 2010 "Flash Crash", and provides profit to connected insiders but no productive economic benefit.
A small tax on all transactions will not hurt economically useful investment, but will discourage harmful, froth-creating speculation.