Restaurants use their own birthday songs, movies rarely include "Happy Birthday", and even kid-oriented radio stations don't play recordings of this song. Are people paying to download it? Where are the royalties coming from?
I don't think it's fair to say these attorneys practice law by boilerplate. Indeed (as Mr. Masnick indicates in his original post), the documents these attorneys have produced do not sound at all like standard legalese -- they seem casual and unique. I don't think I've ever heard of defendants' colleagues referred to as "minions" in a complaint before, for example.
Thinking about whether intellectual property is unethical, you probably already considered this: In most of the world, recognition that government-granted economic privileges aren't based on morality seems to be the basis for distinguishing between "moral rights" of authorship (like the right of an author to be correctly credited for his or her work) and "economic rights". But of course most moral rights aren't recognized in the U.S.