The major flaw was that it is not at all ethical by any means to expose a child and induce fear in him, fear is a harmful element and especially when the subject is a child it becomes more unethical.
This was a famous experiment by John Watson and Rosalie Rayner for which they received much criticism. The child whose name was "Albert" but is famously known as "Little Albert" moved shortly after the experiment so it was a mystery what happened to him until recently when he was found as “Douglas Merritte” who died before he was found.
