Some people don't believe vaccines work and cause autism. Some people believe the earth is flat. Some people seriously believe we are ruled by lizard people. I

Some people don't believe vaccines work and cause autism. Some people believe the earth is flat. Some people seriously believe we are ruled by lizard people. Is it valid? At some point we have to determine what is a minimum acceptable level of cohesiveness in though to take someone seriously. I'm not saying anti-privacy people are in such extreme, but I don't like the 'everything a valid position in the post-modern relativist world'. The line has to be drawn somewhere, and some people might draw it further in or further out. But we all do it.