Are Capitalists Insufficiently Greedy?

Here's a letter to the New York Times:

You support legislation to ease older-workers' ability to prove that they are victims of age discrimination ("Fairness for Older Workers," Sept. 14).

Can you offer one plausible reason why employers would sacrifice profits by firing, or otherwise harming, productive workers simply because these workers are over the age of 50?  Are employers really so soaked with irrational hostility to those of us with graying hair that they need the threat of lawsuits to...