I believe that spanking is a counterproductive means of raising a child, as studies suggest that it leads to heightened aggression and lower IQ and is associated with anxiety disorders, substance abuse, and sexual dysfunction. Separately, I believe that it is immoral to intentionally harm a child, mentally or physically, regardless of what control you wish to exert over them.
Reproductive privacy is a legitimate concern, but perhaps we should debate where to draw the line between that and the child's rights in considering anti-spanking regulation. Interestingly, the same political mind that promotes reproductive privacy in spanking opposes it in abortion and vice versa.

Editorial noting the statistics:
Article citing study: spanking decreases IQ:
Study: spanking at age 3 increases aggressiveness at age 5:
Study: spanking correlated with adult anxiety disorders and substance abuse:
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