An actual fall would be unlikely; It may simply rise at a slower rate. After all, holding the stock /still increases the holder's wealth/. Increasing one's wealth is a strange interpretation of incurring a cost.Supply and demand. The more of something being sold, the lower the equilibrium price falls. If holding stocks incurs a cost, you need to sell.
And if a market is so fragile that it cannot even survive with "only" 80% of the share value growth its currently experiencing, then that's a stupidly fragile bubble, and shouldn't be the basis for a market.
A relatively minor downward force on share price, perhaps, though certainly not precipitating a fall, given those shares still reap dividends.When people are selling, the price falls. Then you aren't taxing anyway. It wouldn't stop market growth entirely, but it would put a downward force on it.
And frankly, I don't give a shit about a small mitigation of the obscene profit margins of 100-millionaires.