A disagreement over the PostgreSQL trademark

I want to make clear that I said they have to do something *here*, I didn't say any trademark holder has to do something in all cases.

While you are completely correct that enforcement is not required around edge cases or people doing minor things, you can actually lose your trademark if you don't enforce it at all. I agree with you that "having to enforce it" is often used as an excuse to be horrible to other people, and I despise that kind of behavior. But in this specific case the other side registered a trademark of the same name (in a different category, but clearly related to the same thing, unlike e.g. the detergent when it comes to the Linux trademark), and that makes a huge difference. If Pepsi started releasing their soda under the Coca-Cola brand without permission, and Coca-Cola did nothing about it for years, they would probably lose their trademark at some point. That's different from a 10 year old kid selling their home-made soda under the name Coca-Cola during a public event, where Coca-Cola would definitely not lose their trademark if they didn't enforce it.