I agree, it's utterly outrageous and a sinister suppression of free speech. It sounds as if Instagram want to emulate Reddit.
I wonder if there's any legal recourse for women who've been banned by them?
As the Reduxx article states, Sex Matters has been judged to be exemplary in their social media conduct. That so, how can Instagram justify their decision? I realise that this isn't as straightforward as an employment case, but once again, an American organisation seems to think that they have carte blanche to trample over UK domestic law.