Noam Shpancer in Quillette:
The scientific case against spanking is one of those rare occasions in which, over a span of 50 years or so, a scientific controversy actually gets resolved, as various programs of increasingly rigorous research converge upon a consensus conclusion.
True, the issue has not been 100% mapped out. Waiting for social science to map any issue out 100% is like waiting for the perfect spouse. You’ll wait forever, pointlessly. Spanking, like any socio-behavioral phenomenon, is bound to have somewhat differing implications depending on multiple variables such as culture, timing, dose, gender, what definition of spanking is used, etc. Local skirmishes about this will continue.
Another hindrance to an air-tight resolution concerns the fact that, due to ethical constraints (you can’t randomly assign parents to spanking and non spanking groups or assign children randomly to parents), true experimentation in this area is all but impossible. In the absence of experimental evidence, causal relations are difficult to establish with certainty. Finding, as we have, that spanking strongly and consistently predicts negative developmental outcome does not in itself settle the question of whether spanking has caused the outcome.
The spanking literature, however, has addressed itself to this problem in several ways.