I will refer to the forums I use the most. Lone parents - someone posts about concerns over contact. There will be responses which imply every problem involved in sorting contact is the woman's fault and the man is entitled to a 50:50 whatever, even if he has been abusive or absent. Then a debate has taken place and the OP who is probably quite worried for whatever reason gets overlooked.
Step-parenting - someone posts but uses the 'wrong' term e.g. skids or bm and it all turns into a debate about that instead of addressing the issues in the OP.
You can always spot from the title the threads which will turn into a fight. Just think it would be good for people to get the advice they need sometimes instead of having their threads predictably hijacked by people with their own agenda.