http://en.wikipedia.org/w/index.php?title=Fallacy_of_the_exc...
The choice is not between saying nothing, and completely devastating that person. Surely there is a third (or even fourth, fifth) alternative.
Also, saying nothing doesn't lead to the belief it is a shitty workplace. Just because someone posting in a forum that he's been fired from Company X for a reason he doesn't understand, that doesn't automatically mean that Company X is wrong and shitty; not everyone jumps to this conclusion, and certainly not based on the absence of any response from Company X.