There appears to be an assumption
... that watching porn will be highly likely to harm children. Is there any credible evidence to support that assumption? IME young kids are pretty much uninterested apart from its forbidden aspect, and older kids use it for the purpose for which it is intended. They also don't regard it as any more true-to-life than a James Bond movie.
Meanwhile, there appears to not be the same amount of hand-wringing regarding the amount of violent content available to children. The message perhaps being, "Make war not love"?