Why do "some" people call others conspiracy theorist?

I applaud your question for its observations of human behavior. I might add that some people are called "conspiracy theorists" simple because they can NEVER come down to a specific answer as to why they think something did or did not happen without including some kind of conspiracy aspect to their answers. These people might fit your label as "smoking wacky backy's", simply because they seem forever unable to accept a direct and simple answer without suspecting some "undiscovered truth" somewhere. It does get a bit rediculous, and as a mental health practitioner with 20+ years experience, now retired, I can say they might also be diagnosable. But, again, I applaud your question for its keen observation of people, and because of my late dad's continual emphasis for us kids to "think for yourself", which was included in your question, and it brought back wonderful memories of the man who would NOT let me just buy the liberal media's bullsheeiiitttttttt. God Bless you.