Well… it’s their site, you have to follow their rules.
I get it - it’s an important historical photo. What if an near identical photo was posted, say some kid getting out of the tub. Near identical image, near identical subject (the naked child), completely different context.
The problem is Facebook has how many millions of users? The pics posted is probably in the billions. How do you police such images? Certainly one wouldn’t want child porn on the site. Certainly even policing “innocent” child nudity is probably prudent. But it takes a person to make such judgement calls on what is and isn’t appropriate - which results in 1) time and money on facebooks end, and 2) inconsistent rulings on what is and is not allowable.
By having this blanket policy they are more or less protecting themselves from illegal images as well as exposing users to unwanted images.
And if this guy was a reporter, you know, you could post it on the newspaper site. Or even post a cropped photo on face book that links to a full article on the news site.