In 2010, Toyota recalled millions of automobiles to fix a potentially hazardous problem known as sudden acceleration. Writing in the Wall Street Journal, James Stewart gave investors the following advice: "Toyota shares were over $90 as recently as Jan. 19, 2010. They closed Tuesday (February 02, 2010) at $78.18, which strikes me as a modest decline under the circumstances. If I owned shares, I’d seize the chance to get out. Required:
Would a believer in the efficient markets theory be likely to follow Stewart's advice?

Of course not. Someone that believes in the efficient market theory (or hypothesis as it is generally called), believes that the market is always right. As an individual investor, you might be right or wrong, but the market as a whole has access to perfect information and the price of each stock already has been determined factoring all possible events and outcomes. I.e. the market's price is always the correct price and there is no way in which an individual investor can make a profit by buying or selling undervalued or overvalued stocks.

Personally, I disagree with this hypothesis, and the reason why most people call is a hypothesis is that they disagree with it. If the market is always right, then this theory is no good.