This is actually the most important point of this case in my opinion. Dont screw over students by going off topic in mandatory courses. Stick to the course material, your ego is not more important then putting an entire course of students at a disadvantage. Mandatory courses are mandatory for a reason, its so the students learn the basic foundation of their field of study. You dont get academic freedom on your mandatory lectures, as your day doesnt consist of only mandatory lectures. Create an elective course on the topic if its interessting to you. Profs who do this are the perfect example for why tenure is a problematic idea. Getting rid of a Professor who is sabotaging required courses is a monstrous task and generations of students have to suffer under the ego of one person.