Fact: etymological knowledge is helpful when you want to enlarge your vocabulary. I will not take exception to it. But what is this knowledge?
Take for example the word "committee." This word is typically analysed etymologically into the verb "commit" and the suffix "-ee." The suffix, so the explanation goes, means the person who receives a certain act, as in "employee," "interviewee," or "referee." Therefore, the word committee originally means the person to whom something is committed. Quite a few students think they have understood the etymology of it after hearing this explanation. They even admire it, saying things like, "Nothing is so eye-opening than this!" But there may be some who raise the question such as: "What about the number of the people? After all, a committee is usually made up of more than one person, right? But the explanation tells nothing about it." In other words, a typical etymological explanation only gives an analysis of a word but it is not sufficient to understand how it has got to assume the meaning it has now. I think that in order to say you know the etymology of a word, you have to know more about it. However, the books about etymology found these days at Japanese bookstores do not provide you with this information. Therefore, I propose that what is called etymology in these books should be called "etymological analysis" and that the name etymology should be reserved for something more than this.