The history of Science is full of people following theories just because "it makes sense." This is where scientific testing comes in. Evidence-based medicine has given us new insight into many diseases that we thought we knew everything about. One of the most powerful aspects is the ability to eliminate multiple variables which may or may not influence the outcome.
As far as composites, are we sure it's safe? Bisphenol A is a known estrogen receptor agonist which leaches out under heat and acidity (both of which are present in the mouth). Estrogen activity in man lowers sperm counts and can even lead to infertility. It can also disrupt neural development in the fetus.