Yes, in their own defense, but not in the defense of others unless they are licensed to practice.
I have heard of a handful of cases (related to immigration law) where persons who offered legal advice were held accountable for providing bad advice online. They did not hold themselves out to be lawyers, but they did hold themselves out to be knowledgeable about immigration law. It's not common for people to be held accountable for this because not many people go so far as to cross the line into "unauthorized practice."
It seems that one of the tests is whether the person offering legal advice is being compensated somehow, and another is whether there is some kind of ongoing relationship. (I'm imagining a scenario where someone offered their services as an "immigration consultant" for a fee, for example, and they made promises that they could help you navigate the red tape of immigration.)
Maybe if one posted enough legal advice on a message board like this one, some kind of pattern could be established, and the person could get into some legal trouble.
I have heard of a handful of cases (related to immigration law) where persons who offered legal advice were held accountable for providing bad advice online. They did not hold themselves out to be lawyers, but they did hold themselves out to be knowledgeable about immigration law. It's not common for people to be held accountable for this because not many people go so far as to cross the line into "unauthorized practice."