I think people underestimate how hard it is to evaluate the validity of ideas. Most people think they are open to new ideas, but actually have a pre-configured bias system that automatically accepts or rejects any incoming ideas. If you are actually willing to entertain new ideas, you have to run with something for a while while you figure out if it makes sense or not. You have to suspend parts of your existing belief system and reexamine assumptions you have made before. You will probably change your conclusion a couple of times in the process.

Dismissing conspiracy theories is the safe thing to do. It also does not require any effort, intelligence or insight on your part. I admire people who are willing to actually engage with ideas like that, even though it does not seem feasible everywhere all the time.