Read 'The Trauma Myth' by Susan Clancy - most children enjoy doing sex, society makes them feel bad about it afterwards. If something is harmless there is no justification for its prohibition.
Clancy is controversial, but she does not (I believe) argue that child sexual abuse is not traumatic, or that any trauma is the result only of social attitudes. Her thesis is that the trauma largely occurs not not at the time of the abuse but in adolescence/adulthood, when the victim attempt to process what has happened to them, in the light of their emerging sexuality.
She argues that the trauma may be intensified by "awfulisation" of the experience by the child's family and community, but not that it attributable solely to that cause. Furthermore, in arguing that child sexual abuse is not experienced as traumatic
at the time, she does not assert that it is not harmful
at the time or later.
Finally, her research is into cases of people who are abused in prepubescence. The great bulk of underage sex prosecutions involve sex with adolescents, not underage children. Clancy's research, and her conclusions, are not directly in point. I don't know whether she would go along with her research being used to support a claim that age-of-consent laws should be repealed, but I suspect not.