Would it be possible to curse an idea or a concept, and have all adherents of that idea get cursed just as they would if you successfully threw it at them individually?
I thought of this topic because there is no other way I am aware of to do a mass curse [and on a specific type of target].
No, because if there was, I’m sure someone somewhere would have cursed all of the stupid people by now 
The main problem that I see with this notion, is that by their very natures, ideas or concepts are not static. They grow and evolve, and change over time, influenced by the consciousness that holds them. There’s no way you could curse an idea and not be influenced by that curse yourself because to even bring the idea to mind in order to cast the curse would in turn enact the curse upon your own consciousness. In order to not be affected by your own curse, you would have to have no memory of the target, because to even bring it to mind would call your own curse down upon you.
Memetics is the study of how ideas spread, and one of the theories is that they propagate themselves in similar ways to a virus. As we all know, viruses evolve, and what kills one form of a virus will not kill another. All it takes is a simple twist in DNA to make a vaccine useless. In my opinion, this would also happen if you tried to curse an idea or concept. Your curse might possibly have an effect on any consciousness holding the original version of the concept or idea, but it would not effect any subsequent evolution of it.
Your insight is deep 
I disagree because all the stupid people would just curse us all because we are all part of the stupid people problem in one way or another. But if you create a sigil for the spirit of an ideology that might be something. It has been something I’ve been considering for a while now. If you can invoke the internet you can probably curse an idea or concept.
I would try to be just a bit more specific in your cursing. Instead of an entire ideology, try for specific groups or departments that embody or practice it.Vaguely cursing an ideology is too broad, too many people to take out.
Cursing “stupid people” is terrible because guess what? We are all a bit stupid sometimes, you’d end up cursing yourself.
Be more specific: what exactly do “stupid people” think or do? What organizations do they work for or participate in? What, to you, are “stupid people?” It is very important you are clear on that for your magick to be effective.
If it was me/ using myself as an example: my idea of stupid people includes (but is not limited to) all forms of government. You can’t practically curse an entire government (I’ve tried. In retrospect I would have needed more people to make that one work).
But what I can do is curse specific departments of government, or specific ministers or states people- and that I have done to great effect.
The key is to be more specific and break up the target into more manageable pieces.
What concept are you trying to target, if you don’t mind my asking? Depending on what it is it might be easier to shift people’s attitudes about the concept than attack the concept directly. Take the idea of slavery for example: go back a few hundred years and most people had no problem with the concept, but nowadays it’s pretty nonexistent in the ideosphere.
There should be a way to “poison the well”
but I think it would be easier to curse some source of spirituality and emotions (poison the water)
as different to curse an idea (“poison the air” it would need a “pest” I think it would become harder)
so I guess it would be easier to curse the sourse of “water” their spirituallity or emotions