Most of us just want to fit in, and believe what everybody believes.
Coming to your beliefs this way is not actually intelligent. We don’t do it consciously. It’s just tribalism or herding instinct or whatever.
So if everybody agrees with you then that’s a pretty good sign that you are wrong.
A contrarian isn’t one who always objects — that’s a confirmist of a different sort. A contrarian reasons independently, from the ground up, and resists pressure to conform.