This question is too complex to be answered so categorically. First, there are no absolutely stupid people, one way or another, you can learn something from everyone. In my opinion, the mind is a certain ability, skill, it is not in vain that it can be "honed", like any other activity. You've probably noticed more than once that if you haven't done something for a long time, you will lose this skill. In the same way, with the mind in the case of communication with a person, at a level that does not quite correspond to yours - you simply do not train him, and this skill in the same way over time goes to the periphery, giving way to more relevant and necessary skills in this communication (social and so on).
So, if you communicate with such people for a couple of months, after some not very long time you will again return to your position of "smart person". The longer, the worse the return will be, because why should your psyche keep a skill that is unnecessary and irrelevant?
is possible, and very simple. communicating with a stupid person, you see his low level and stop raising yours - you are already above the stupid person. and development with the progress of the individual is inhibited, and the further - the stronger. and then, continuing to communicate with the stupid person, you condescend to his level in order to be able to communicate. degradation is evident.