alt Hacker NewsI'm the author of the original article, I'm a tenured professor, and none of these things is optional for me. Indeed, I wrote this article several years into being a full professor, because my obligations had only grown, not reduced, by virtue of all the promotions. Of course different people have different senses of how "obliged" they are or should be.
It is important to clarify what we mean by "obligated / not optional", as I think there is a terminology mismatch.
When I said that a particular job task is not optional I mean that not doing this task will lead to a disciplinary action from the employer (being fired, put on a performance improvement clock with the HR, etc.). Reducing those tasks brings in one set of considerations.
Your definition of "obliged", if I understand it correctly, is primarily a self-assigned or a community-expected one: "if I stop running this seminar or remove myself from that editorial board, I will feel I am not doing all I can / my colleagues will look at me askance". But it will not trigger retaliation from the employer. Reducing overload from those tasks brings a completely different set of considerations.