The market makers win on both factors. Their concern is that my sell order will be followed by many other orders to sell, because that would leave them with a l

The market makers win on both factors. Their concern is that my sell order will be followed by many other orders to sell, because that would leave them with a large inventory of stock that they can't unload except at a loss (because the market impact of that selling probably drove the price down). That concern might exist because I'm selling a big position and my order is the tip of that iceberg, as you say; but it could also exist because I'm trading on news that hasn't yet been incorporated into the share price, and my order will be followed by many other people selling once they learn that news themselves.