> I don't think I disagree with you generally, but it must be recognized that trademarks are different from copyrights in that there is a mechanism where if you don't assert your rights in the trademarks you could lose them.
That sounds exactly like you disagree, and not just with me but with reality.
When this discussion topic arises, the most common thing people leap to is genericization - it is possible that if basically everybody calls this thing a Doodad when you one day sue some company to stop them using your Doodad trademark to describe their product, the judge says that's just what everybody calls these thing so you lose. But: One: This happens when you're a tremendous success! Most businesses would kill to have a product as widely known as Xerox copiers or the Hoover vacuum cleaner. Two: You can't fix this with lawsuits anyway, the judges are looking at what everybody calls the product, and you're not going to sue everybody and even if you sue movie stars and TV hosts you won't change what everybody else calls it.
Next most common are people's half memories of the 20th century trademark restitutions from World War I and World War II Germany. German industrial firms as "punishment" for their role in these conflicts had their marks invalidated in some cases. So you might well find that some mark which is protected in say, Venezuela or Japan is just generic in the United States or say France, because they won the war. In a fuzzy memory this somehow becomes the Germans "failing" to protect their marks, just conveniently in the immediate aftermath of a war, hmm, I wonder why it's only German companies, why they "failed" to do this and only in countries they'd just lost a war against...
Finally Estoppel. Estoppel isn't special to trademarks, it's a general principle in civil law about you can't tell people they can do X and then sue them for doing it. If Disney allowed primary schools to do a Little Mermaid play that's blatantly just the script of the original cartoon movie, and then one day they pick on the play at Little Nowhere Infant School and decide to sue, the lawyers for the school (if it can afford them and doesn't just settle) would argue that's Estopped, there's a long standing understanding that it's OK for schools to do this. Estoppel has practical limits so it's not a real threat and is often over-inflated by IP lawyers. So e.g. if Little Nowhere is selling a stream of the play that's not what Disney agreed to allow, or maybe the Little Nowhere "Infant" school somehow has adult actors and a huge live audience which makes $$$ on ticket sales, again a judge can see this is not what Disney envisioned, so they're entitled to sue anyway.