How about the pitcher doesn't get into a 3-0 count in the first place? It shouldn't be up to the hitter to give the pitcher a break.
Also in a time where stats matter when it comes to MVP awards, batting titles, etc. that directly effect your next contract, why shouldn't he be swinging at a meatball?
Like others have said crazy things happen in baseball, no lead is truly safe until the 27th out.
And how are people going to compare football to baseball? In football, even just one extra play could lead to the end of someone's career, it is more about safety then running up the score IMO.