So the blue cross people were doing what they had to do. It sure is funny though how almost every law is interpreted in a way that maximizes future legal work involved.
This is mostly false as a concept, and false as written. It's pretty much a fiction trademark lawyers use to try to convince people they really like them, but they have to be suing them now.
There is no special "if you don't sue people, you lose" defense for trademarks, on that front it's the same laches defense as anything else.
About the only thing you risk is loss of distinctiveness, and only then if you are not otherwise doing things to try to maintain brand distinctiveness.
In fact, there is a specific "doctrine of progressive encroachment" that allows you to let people minimally invade, and only sue for infringement when there use expands past something small and minimal.
Even in cases where all of this fails, nobody has "lost a mark" except to genericness (which is unpreventable, in reality). The last case i'm aware of to confront this issue, the defendant was still barred from using the mark in the future, the plaintiff just got no money damages.
boo hoo.
There are a fairly limited number of useful marks because companies need fairly short names. Imagine if trademarks worked like copyright and modern companies had to worry about infringing the mark of a company that hasn't traded since 1940?
If patent enforcement worked like trademark enforcement, then trolls would have a much harder time.