With something like polyamory, which has no legal protection in many states/countries from discrimination in regard to housing or employment or custody of children, I think it is probably reasonable to ask that some things be deleted in an event like Pliglet is talking about.
Someone stalking and using posts on a website to try to hurt someone in a poly relationship by showing this information to employers or lawyers is kind of above and beyond what someone can normally expect on a message board. Yes it is bad to post your name and address and telephone number to make sure that kind of private information doesn't go out public, but in order to prevent someone who knows you from finding out who you are, you might have to strike out quite a bit of the kind of personal detail we usually ask for and need to give good advice. This includes things like the sex, gender, number, and ages of partners, the fact that kids are there or not and if there is a divorce situation with them, and sometimes even generic information like what state you live in.
These aren't things I would reasonably withhold from posting here usually, but if, for instance, my in laws found out and my future husband and I had kids together and they wanted to use my posts on this website against us in trying to declare us unfit parents, it probably wouldn't be too difficult if they really wanted to try. If I found out they were doing something like that, I might want some of my posts removed in order to protect my children from them, even though I've posted nothing unreasonable.
I guess what I am saying is that in an extreme stalking situation, it isn't the fault of the poster who posts reasonable levels of personal information if someone is maliciously trying to hurt them through a legal system that does not understand or support our way of life. In many states, at-will employment means that they don't even need cold hard proof to fire you for anything. They can just have a suspicion that "you aren't a good fit there."
In most cases, yes, I think that people should be responsible for what they post, but in cases where peoples lives are at stake and they haven't really done anything wrong, I would feel that it would be rather callous and cruel to just sit back, throw your hands up, and go "Welp, you posted it" when you are fully capable of removing some of the material to help them out of their situation.