It falls into a place never envisioned by those writing the amendments. When you have defacto monopolization of the public media, or even a major portion of it under your control, then preventing commentary is functionally censorship equal to if the government outright banned it.

On the other end you have the desire to prevent harmful transmissions to the public space as well. Incitements to violence and propagation of blatant lies serves no good purpose.

Balancing the two has been the subject of countless lawsuits. The only justification I could see here, given the visual nature of Instagram, would be the potential for gore and violence content. Sometimes showing the ugly reality is needed to let people know the reality rather than a polished sanitized version. Instagram might not be the place for that though given the audience it has.

By comparison a tame subject, but the case involving George Carlin still holds some sway on matters of what's appropriate for public broadcast.

https://en.m.wikipedia.org/wiki/FCC_v._Pacifica_Foundation