First of all, even if a conspiracy theory is true, it still is a conspiracy theory. Just like a scientific theory doesn't stop to be a theory, even if the evidence is so immense, that it's accepted as fact.
Second: It is pretty clear, which conspiracy theories David is talking about, if you actually listen to what he says in the video. I quote: "When there is a mass-shooting, there are these elements from the internet and from the Alex Jones show, that claim, that the events where staged with actors." So a much more clearer definition than what you claim, at least 9/11 can't possibly in any way be 'lumped in' with it.
And third which 9/11 conspiracy exactly do you believe to be fact and where is the evidence for that? It is btw lovely, how you assert you are right about something most people have a different opinion on without providing evidence first.