The problem I see with that is that it would probably turn into a CSRF attack vector (someone could post a link somewhere that executes some action in discourse, and anyone who clicked would have that action applied to their account, if they are authenticated in the discourse site pointed by the link). The link could be masked as a short link too, like bit.ly/some-key.
In most cases (or all?), GET requests should not change state. That said, such a problem (CSRF vulnerability) could be avoided, or at least mitigated, if the link requires a token generated by a moderator (or admin), to execute a specific action (related to the token), but I don’t know if it justifies the effort, although in cases like you pointed it may be useful (especially for people that don’t know how to navigate the internet very well).