It's a good point nbeans. There are three elements to defamation: (1) identity (2) harms reputation and (3) communicated to more than one person.
The last two are beyond doubt. So can someone using a pseudonym whose reputation is lowered on a public forum still be defamed? The answer is yes (see: Baglow v. Smith, 2015 ONSC 1175 (CanLII)), however, it would be necessary for me to show that my true identity is known amongst more than one regular reader of this forum. Don can take the risk that I haven't had other communications with many readers here, both before and after I joined, and that they know my real identity.
Don also tries to hide behind the words "seems to me". Again a good argument on the face of it. However, once again case law shows this depends entirely upon whether a reader of Don's false statement would reasonably believe it to be true. There is ample evidence that more than one person here would reasonably believe what Don claims. (Don essentially admits this with his claim that others have said worse.)
Don can take the risk of not accepting my terms for the consequences of his defamation, that I don't have the time, resources or expertise to pursue other consequences. This would be a mistake, especially as not only do I know Don's real identity (something he has never hidden) but the fact that he shows no remorse for defaming me will only compound the consequences. In fact I can show that not only do I know who Don is but he, without realising, also knows me. We go back many years.
There is an easy solution, Don, you know what you said is something you have no idea about the veracity and you know that many people here will trust your views. Even if you are not worried about what I will do, you owe it to yourself to admit you have no idea about my motives and even less idea as to whether I mean any harm to shareholders. Oh and an apology for your rash statement is something the Don I know would give unequivocally.