Coulomb's law -- like the notion of absolute zero -- is based on an extrapolation.
It is possible that the rule of repulsion between like charges and the rule of attraction between opposite charges does not hold for very small scales. Instead, suppose the relationship between certain charge combinations was the net effect of two underlying attractive and repulsive tendencies. Ordinarily for opposite charges this would manifest as a net attraction above a certain distance and for similar charges as a net repulsion above a certain distance. Below a certain distance opposite charges would become more repulsive and similar charges would become more attractive. This new rule would not alter the identity of the charge, i.e. it does not violate charge conservation. Harry
