I've heard this argument made (I believe I've even made it myself at some point), but in practice, it turns out to be less effective than people think. "Be silent and it'll just blow over" is increasingly ineffective as a strategy because the Internet has a longer memory; as one looks up information on a person, allegations will jump to the surface. And increasingly, people seem to assume that absence of a counterpoint is implicit admission of possible truth (there's the perpetual "when will you stop beating your wife" argument, but a lot of other allegations are in far more plausible categories, where silence can imply a lack of ability to defend one's reputation).
I agree with what you're saying there, but instead of responding by apologizing people are often still better off by going on the attack, calling the allegations baseless nonsense, or personally attacking the people spreading them.
