If I had 50,000 dollars I would definitely invest a portion of it in the stock market. I wouldn't invest the full amount because the stock market is not exactly known to be predictable, however I feel that a few knowledgeable investments couldn't hurt. As long as you're investing wisely, the stock market can be quite prosperous.
If I had $50,000 in emergency savings I would not feel comfortable investing it in stocks. I know very little about stock market and I am not big risk taker so it would be quite unreasonable for me to put money, especially money that was meant for unpredictable situations, into something that risky.
I disagree that my emergency savings should be spent on something that might flop in the next second. My emergency savings could save my life and be a good back up plan for/ if things get sour in my life. Stocks in my opinion are a bad thing and I would never invest in such a thing.
There are times in life when having a reserve of cash for an emergency is essential. If I had 50,000 it wouldn't be wise to invest in stocks as the markets are too volatile. Plus getting it out of the markets could offer penalties. People who have emergency money should hold on to it in case something should happen unexpectedly.