Calling attention to factual errors is good.
Criticizing an author personally and calling his reputation in his
specialty in question on all his work due to tangential items is bad.
Always bring errors out, but never make attacks on an individual.  It is
bad scientific proceedure.
 
Everyone makes errors. It is not usually fatal, and should be easily
admitable, but does not necessarily call for a published admission.  By
the rules intimated, not challanging the correction amounts to agreement
with the correction.
 
As to things in printed publications going without corrections:  The
overwhelming majority of readers have never written about errors they
note, giving a suggested correction, and have never written an article.
 The absence of a correction is usually no confirmation of facts.
Consider your daily newspaper.  Frequently,  pertinent facts are
incorrect, or missing, or misleading.  It doesn't mean stopping reading
the newspaper.
 
Aloha,
 
Wes