Was 1987 so long ago that no one remembers portfolio insurance? Was the flash crash so long ago no one remembers?
The situation depends somewhat on what market you're trading. If you're talking about US equities, there is no reason to put in market orders. Current US equity markets are based largely on the original Island ECN, which didn't even allow market orders. The exchanges bought Island and similar ECN's, and patched in what the (clueless) investing public wanted -- "market orders". But now you take a huge risk every time you submit one. With a market order, you may buy at $199,999.00 or sell at $.0001, regardless of the true value of the stock. Trades at such prices go through more frequently than you might think. If you're on the wrong side of this, you'll likely get the trade busted (if you act in time), or you may not. If you put in an appropriate limit price on your order, even if it's an executable price, then this problem goes away.