Some movements that claim to be religious do attract and encourage unhealthy mental atitudes, certainly.
That is a good reason to be more rigorous with the use of the word, IMO. Not so much to toss the good work together with the unhealthy movements.
That aside, I fail to see how those could actually make people stupid as such. Discourage necessary questioning I can see. Create environments that spread misinformation, superstition and obscurantism, certainly (I am looking at you, Creationism). But that is not quite the same thing.
It seems to me that you may be confusing cause with effect somewhat,
@psychoslice .
To a considerable degree, the lure of voluntary retreat from rationality is a result of psychological fragility. It may also feed back into it, of course, and we should watch for that and attempt to heal such situations.
But it is not like there is some convenient, well-delimited "religious switch" that might conceivably be turned off and make it all better. The fragility is real and we should acknowledge that there is such a thing as healthy religion and encourage and support it. Nor is it easily delimited, either; quite a lot of religious practice is to some extent unconscious "heresy" that rises above the level of the received doctrine.
But most of all, I think that when you propose that religion may be harmful you should take some care to clarify what you mean by religion and what you propose as a likely or desirable alternative.
I take it for granted that you are not proposing that religious groups should be outlawed, nor murdered. I hope you realize that it is not really possible to command people into "non-religiosity", however you might define that. I trust you are not proposing that people should be forced to practice in secrecy. But all of those unlikely scenarios might be assumed by a casual reader, so it is worth mentioning them and clarifying why they do not apply.
From past experience, I assume that the general gist of what you favor is that people should be more skeptical, value and pursue their personal freedoms, and refuse to take supposedly religious authority very seriously. There is definitely something to that. But that is very different from simple avoidance of religion.