What is the usual etiquette re “thread hijacking”

I don’t think I’ve ever done this on purpose...

If you strongly disagree with something do you just muzzle yourself?

Or do you try to express your opinion politely?

How much is it frowned on by posters? “Hijacking” of threads

Do I come across as a rude and selfish person?

If I’m not rude and selfish I haven’t done a bad job on my self work since all the family of origin were (and are) abusers (malignant Narcissists)