One of the most dangerous and unethical practices of Dr. Watson was the use of infants and non-consensual minors to experiment on the removal of a phobia. The American Psychological Association is highly strict in that children must have a permission from the Institutional Review Board (IRB) that is sponsoring an investigation prior to even considering using a child as part of any type of study.
Second, he did some heck of experiments with them by dissociating them from what they knew, and turning it into something bad: For example, stuffed animals would "become" monsters and sudden noises would disrupt the mental peace of the children, mostly infants. Therefore, this man was literally making these children insane.
Yet, he is the precursor of BF Skinner, and hence the grandfather of behaviorism.