Conspiracy theories are mostly an exercise in back-fitting events to support a desired belief. I think there is a psychological need to find an answer – any answer to unnerving questions so people come up with conspiracies to satisfy that need. If you need a conspiracy theory to maintain your belief, you may want to rethink that belief because it is on some very thin ice. Your belief is now using its final, most powerful trick to stay in your head. It owns you.
In my mind there are no “Grand Conspiracies.” They would collapse under their own weight because people can’t shut up that long. Ancient Aliens, The Illuminati and most government conspiracies can be adequately explained by mundane actions and processes but that’s no fun. Let’s come up with the most outrageous scenario possible, back-fit facts and make up “evidence” and see if we can make ourselves believe it! Now that’s fun! Delusions are just another type of drug allowing us to avoid reality.
Seeking the truth is difficult and reality is uncomfortable that’s why we avoid them like the plague. Therefore conspiracy theories should be seen as just another form of self-medication.
As said, there is a difference between thinking about them and believing them in the same way there are truths to be found in the bible or in Shakespeare, there is also a lot of artistic licence in both. Reading them doesn't do the harm or the good, it is the resulting actions.