‘What is freedom of expression? Without the freedom to offend, it ceases to exist’, Salman Rushdie.
But the corollary to this credo would be...
Those who exercise the right to offend lose the right to thin-skinned whining.
Outing somebody's pen name is a pretty serious step, because there can be a lot of legitimate reasons for using one.
On the other hand, regarding those who blog under their own names (and therefore accept direct accountability for what they publish), there probably is a limit to the number of times some people are willing to read juvenile name-calling because they happen to disagree with policy positions.
"Dissent is the highest form of patriotism." Secretary of State Hillary Clinton