Which conspiracy theories are the easiest to get your head around?

This is kind of a paradox given that the very nature of a conspiracy theory involves a person questioning what he/she believes about a certain event and during this process you feel uncomfortable or even angry at someone. People basically hate getting lied to.

I think it is healthy to question things that most people simply just accept as the truth. More often than not you learn valuable life lessons about yourself as well as about human nature.
After all, Aristotle said:

So anyway, I would like some input as to which conspiracy theories are "not so far fetched" or "easy to explain and to verify" or a stepping stone to some of the other "weightier" conspiracies.

Now, I don't necessarily believe the conspiracies I am going to list but I have researched most of them quite a bit. I recently talked with a friend and the conversation somehow ended up with conspiracy theories but I didn't want to bombard her with blatantly unnerving thoughts. Here is my list sorted from "easiest to prove" to the hardest and most outrageous conspiracies:

1 - 9/11 (maybe one of the most famous false flag attacks)
2 - Gulf of Tonkin incident
3 - CIA programs eg.
- Operation Northwoods (Cuban war justification)
- MK Ultra
- Operation Mockingbird (Media propaganda in the 50's)

4 - Health related conspiracies:
- Fluoridation of water
- Chemtrails
- Junk food
- certain drugs like alcohol being legal but cannabis being illegal

5 - The moon landing
6 - Alternative history: ("History is written by the victor")
- World war 1 and 2 (Holocaust and Hitler)

7 - Zionism: Group of elite Jews (not all Jews) who controls
- the money supply (Rothschilds) - Federal reserve and other central banks
- Hollywood (moral decay for the most part)
- the media (News channels and newspapers)
- entire countries like the USA

8 - Flat earth (this one is quite difficult)

I don't want to make the list unbearably long so ill stop there. What are your thoughts on conspiracies in general and which would you first talk to people about if they are new to questioning things?

Thank you for reading!