If you believe that exercising is dangerous, a few incidents of people dying from exercising are enough to reaffirm your conviction. You will conveniently disregard those who become decrepit because of lack of exercising.
It is hard to unlearn what we’ve learned to be the truth. But, without continuous relearning, our knowledge is confined within what was unfolded from the present technologies and limited expertise.
Scientists thought Pluto was a planet until further discovery revealed that it wasn't. Even Scientists are fallible, let alone us.