You can read in the history books ( and I have) that these laws were pushed hard by the relevant professional associations. But the motives are a matter of interpretation. They aren't going to come out and say, "We want to establish legal education requirements so that we can make more money". The argument they make is that we need to make sure everyone is "qualified." Perhaps they were being sincere, perhaps not. But if even if they were wrong out of ignorance, the idea could out compete the truth because it has a built in ratchet affect.

So we might not be able to determine the absolute truth, but we can still do significantly better than taking a wild-ass guess.

One should certainly read such books (if you care enough). They almost certainly have useful information in them.

But read them critically. Most such books are written by "natives" rather than by dispassionate observers. A book on "history of education" is almost certainly written by an educator who is interested in history. Such a person will tend be less critical about the value of education than an outsider.

There are similar problems in some other subfields (e.g. history of labor/unions), and of course anthropology (most people studying the Navajo tend to like Navajo culture and have "gone native" in some sense).

[edit: emphasized word Most in response to next comment]

"Such a person will tend be less critical about the value of education than an outsider."

Check out John Taylor Gatto's book The Underground History of American Education.

C.f. also http://www.cantrip.org/gatto.html