Interesting thoughts Peter. As the Admin of this friendly group I'd like to offer up a varying point of view.
There is is great joy in giving without expecting anything in return, and many members subscribe to this philosophy. In addition, when you teach/share your own knowledge is usually strengthened, so you ARE getting something in return.

Obviously is someone is bringing you down with rude comments, or bad attitude block them.

But if they are not 'bothering' you, blocking them because you feel they are giving you 'nothing' might well be shortsighted. Just my two cents.