There are many kinds. But one particular kind:
I don't care who they are, unless the initiative is reversed, those who love to ask others to study or to teach without compensations, but study not or teach not themselves, are of the lowest class of society's garbage. Regardless of their excuses, which could range from: "Oh I'm too old or it's too late, Oh I only manage or direct people, Oh I don't have the talent" to "oh younger people should do it more, oh I only want what's better for their future".
Of course, in some cases, it is enough that we just suffer them, there's no point in quarrelling with these garbage.
However, we must never accept their praises and their help or supports so that their effort is discredited, which is a must, for such vain efforts may be used by us in all wisdom, not guile, but the values are next to nothing.
Then what are they to do? They can either do those things they tell others to do, or they could shut up.
The reason I view it such way is because the kind of society's garbage by common view can easily be changed into better persons, much easier than these mules.