I think one of the things that fundamentally bothers me when conspiracy theorists get into scientific topics is the basic laziness of it.
There are a lot of things about the universe that are hard to understand or that nobody understands, but to a remarkable extent it's basically an open book. It takes a lot of effort though. It works in complicated and subtle ways that the human brain isn't trivially suited to comprehend. Trying to understand all that is a huge adventure.
These people imagine that all of the big questions of existence have easy peasy answers but that they only seem hard because someone is deliberately hiding the answers from them, like some annoying nerd who won't let them copy their homework. We got the answers all handed to us on a silver platter but they're locked up in a government warehouse somewhere next to the Ark of the Covenant.