Facebook remove images of breast even if they are mothers breast-feeding infants.

Youtube doesn't allow breasts.

A US TV outrage happened because of one partially uncovered breast during a sport event.

Yes, some people are shocked by that sort of content. Legitimate is secondary; if they own the computers you're using and they have power to dismiss you it's a good idea to think of their reasonable requests as legitimate.

Sounds like a US centric thing then, most countries in europe AFAIK will allow breasts to be shown in prime time TV as long as the context is not overtly sexual.

Edit: I've definitely seen breasts on youtube

Youtube allows breasts and nudity when used as an art form - not in a pornographic sense.

I guess your grandparents are pretty progressive, then?