To be absolutely fair, I have seen something similar to the "you knew what you were getting into" accusation on a fairly regular basis in other areas of MN ...... one is when a woman in an abusive relationship with kids gets asked why she had (more) kids with the perpetrator and another is when someone in financial difficulty gets asked why they have children when they "can't afford" them. In both cases, I feel such comments are rather like shutting the door after the horse has bolted, the OP can't turn back time, and there are a lot of assumptions intrinsic in such remarks i.e. that people's circumstances were exactly the same as the situation they're writing about now and that things can't possibly have changed. I'm always reminded of the "you knew what you were getting into" flung at stepmums then because it's so utterly unsupportive, potentially designed to make someone feel even worse than they already do, misses the point of the OP completely because such replies are designed to attack rather than actually address the issue at hand and imply that people "deserve" what they get because, shock horror, they weren't fortunate enough to have the gift of seeing into the future.
It's funny, because in real life I'm pretty thin skinned and am easily hurt by spiteful goady remarks. Online though I seem to be able to cope with the snipes I've sometimes had on MN - though I get very angry on behalf of other stepmums who I see getting a hard time of it with irrelevant spite thrown at them. Personally ..... I really do feel able to pretty much wash it off by thinking no-one on MN actually knows me, and vice versa, and therefore what do their opinions matter ? Having said that I can fully appreciate that some threads which are derailed by petty criticism would be very upsetting for a stepmum at the end of her tether - and particularly so for someone who'd ventured online for the first time to try and find help and support. IME, most step threads - even those posted elsewhere on the boards (my heart always sinks if I see someone has been brave enough (or naiive enough ??) to post a step related thread on AIBU - are soon enough found by people who do have step experience of their own and who are therefore usually fair and sympathetic, and for me, they cancel out any other posters who seem to be there for no other reason than to shit stir.
I will confess to being a bit of a hypocrite though ..... I'm afraid that although I've never said anything dishonest about my situation, I do "hold back" on both the full details of it on here, and, the depths of my own feelings because it's a public forum most importantly - and could therefore potentially be read by my stepkids, their (awful) mother, my partner, and any other person who might just know the family and be able to identify me. And also, I admit, that although I feel confident enough to cope with any barbs received as a result of what I already post, I don't relish the absolute kicking I'd get if I vented what I sometimes feel in full technicolour glory .... I know there'd be one hell of a lot of pearl clutching if I did that because this situation, more than any other in my life, and one which has been going on for well over a decade and is still having a significant effect on my life (and more importantly that of my child) is one which gives me the absolute rage and the thoughts that can roll round inside my head are extremely forthright and sweary indeed.
Someone upthread suggested the British Second Wives Club (BSWC) and I'd agree that if you want a place to vent honestly, and where you nearly always get great support (if you're being unreasonable, people will let you know, but fairly - without the hysteria) that's the place to go. I've been involved with them and have used their boards on a regular basis for almost 9 years - and perhaps having that place of safety means I'm less likely to feel terribly hurt by any MN sniping ? It's as about a safe a place as you can get .... it's members only and applications are vetted. Members can supply the admin team with the name and address of people (plus an explanation) they wouldn't like to join the site because it would compromise their privacy and potentially cause trouble .... so, your partner's ex might be the obvious example of that, but you could also suggest your MIL or the ex's relatives if, for example, you'd already had them "stalking" you online (e.g. Facebook) and "spying" for want of a better description by passing info about you and/or your life onto the ex who has then used that to cause problems. Anyway, whatever your reason for wanting to block someone else, it's taken seriously and therefore most members feel safe to be very honest - which, in itself, when you are stressed to the nines, is very therapeutic even if the original problem(s) aren't solved. It's true there's no swearing allowed but there are plenty of emoticons you can use in place of swearwords and I think that's a fair exchange - to respect other members who'd otherwise be put off by the language for a place where you can be yourself without fearing someone who wishes you harm is going to find you.
Just to end ...... while I totally appreciate (having been there myself in the past with a cheating partner) that seeing an OW write can be triggering for those who've been cheated on, I don't think that even if someone is an OW that every scenario she might find herself in is therefore automatically deserving of brickbats. I've seen posters who admitted to being OW absolutely vilified when they were seeking help - for example - for stepkids who were being subjected to really bad alienation. Yes - on the one hand you can see the abandoned partner would feel justifiably hurt, angry, shocked etc but IMO there's never any justification for using kids as weapons and damaging them won't achieve "revenge" on the OW will it ? So, you have a poster who admits to doing "wrong" in the past but whose questions about how they can make the future as good as it can be are utterly ignored while she's screeched at along the lines of "no wonder the ex is acting like that". Well .... errmm, okay, but kind of missing the point. Life is never simple, and to be blunt, "shit happens" .... not necessarily right or fair, but surely the only way forward after that is to make life the best it can be for all involved - and of course, particularly so for any kids involved. You can argue till the cows come home about whether or not an affair was "justified" but most people's lives are pretty "grey" rather than being obviously black or white and in the meantime, if you concentrate on attributing blame and attacking the people seen as guilty, the actual reality of the new situation is carrying on regardless and steps which could potentially be taken to help smooth things over a little are being missed because people are too busy arguing. I hope I haven't offended anyone and that some of you reading this will have an inkling of what I mean ...... it's like someone who admits to being OW says I feel very worried about my OH because his ex won't let him see the kids, and instead of her being offered constructive advice about how her OH might handle the situation sensitively, she just gets a load of verbal attacks and meanwhile, her OH still doesn't see his kids, and those kids still don't get to see their dad. Maybe dad "deserves" to be miserable, maybe OW "deserves to be too, but the kids don't and regardless of how badly those adults might have behaved surely the decent thing to do is to offer support for the children in a practical way rather than just say "you shouldn't have done it, and you've ruined those kids' lives" because that solves nothing and while no-one would wish a split upon kids, and especially not a particularly messy one, sometimes, IMO, the best thing is to get on with making the future better given you can't turn the clock back.
That turned into a rather long whitter, but thing is, I don't always think that the state of being OW is relevant to the question in hand. It might help explain why an ex is being so difficult, or causing so much trouble and of course it might explain why children are so hostile. But having established that fact the original question can then sometimes get lost in the flurry of righteous indignation - and all the pearl clutching in the world isn't going to help kids struggling with what's happened is it ?