It's a tactic to undermine your position without bothering to address the argument itself. Sometimes it comes up when the original post reeks of amateur hour or an individual has grown tired of debating self-proclaimed experts who read the Wikipedia page five minutes earlier. It's sometimes possible to get the debate back on track, but for the most part you're dealing with a debate tactic. You can have a meta-debate over whether such authority is necessary, but by that point you're far off course.

A logical debate can only take place when both sides agree and bind themselves by the appropriate rules. Unfortunately, many who debate online are not willing to engage on these terms.