There are reputable teachers and I'm not sure that I've seen that statement disputed. BP actually has as many or more teachers than students in my opinion. Not all of the people whom I believe to be teachers are advertising themselves as such though.
Anyway, about the "Gurus". I think there are a few common complaints: people pay money to be taught that they can invest with no money; despite the fact that this statement is highly misleading, if you're at the seminar, you've already spent money. Also, I can always tell when there has been a seminar in my city because the street corners are littered with new bandit signs, CL is cluttered with new ads, and my inbox is full of emails from people trying to sell me properties that they don't have. I think it's great that people are getting motivated to get started but they're being told or they perceive that they're being told to mislead people. I could find probably 20 examples from the past 5 days on BP where new people sign up and their first post says "cash buyers wanted, huge inventory, act fast" or whatever. I reach out to some of these people to learn from them about how they acquired their huge inventory only to find out that they don't have a single property under contract; for many of them this has been their first attempt at advertising or marketing of any kind.
I don't lump all new investors (I am one myself) or all gurus together but I can definitely tell which new investors have just attended a guru seminar.