I think this is a problem with modal logic. There are important nuances between what is true, what is likely and what is possible. In my experience, people are not good at perceiving those nuances and personal bias often erases them. It can go in one of two ways: (1) It is possible and I like the idea so it is true; (2) It is possible but I do not like the idea so it is false. Now what happens when lots of people indulge in (1) for a particular topic (here the lab leak hypothesis) ? Then you will have lots of "serious" people forcefully pointing out correctly that there is no evidence that this is true, since it is merely a possibility. But since people do not perceive the nuance, they will interpret that as meaning that the "serious" people believe it to be false. When the group indulging in (1) stops monopolizing the conversation, the nuance reemerges and it appears like it becomes a possibility again.