I dunno actually - this is a business, responsible for a lot of people's livelihoods, and it's owned by Justine et al, it's not some kind of online commune. Posie was told again and again and again what the rules are, and decided not to abide by them. It's like me coming round your house, being told politely what your house rules are, and then deliberately ignoring them. It's rude and unnecessary.
I think MN can't please everyone - they're trying really hard to allow spirited and robust debate, whilst maintaining a business and, importantly, trying not to get sued. Getting sued is stressful, expensive and time-consuming. Getting criticised by both sides is, as @MNHQ have pointed out, morale-sapping and exhausting. They're trying to be fair and balanced, and nothing they do is ever good enough for some of you.
I don't know which posts/patterns of behaviour were responsible for Posie & Lang getting banned, and nor do any of you. MNing isn't compulsory - if you don't like it here, you can leave. But I really hope you stay. It's (for the most part) a fantastic place where women support each other and can talk freely about our rights (and threats to those rights). MNers over the years have saved me from suicide, supported me through years of infertility and miscarriages, and made me laugh and cry more times than I can count. It's where I learned that I'm a rights-hoarding dinosaur, a TERF, and a complete slob for not washing my bed linen twice a day. Is it perfect? No. But then none of us are, either.