MN to an extent protects its users and has this as an understanding with users. (Not so much policy or rule but a general concept)
If threads go libelous they will remove them to protect itself but also to protect users.
You are potentially at risk of someone going legal on you if you post libelous and harassing stuff - MN try and keep things to 'in the public interest to discuss' rather than go that far.
This limits the risk of lawyers coming and asking for information to track down individual posters (and thus protects anonymity).
The assumption from MN tends to air on the side of assuming posters may not realise they are going to far so acts almost like a guardian to protect them.
Whereas on tattlelife (and twitter /Facebook to an extent) the risk is more personal to users. This isn't a hard and fast rule as you are still responsible for posts on MN and they could come back and haunt you but it's less of a risk being of MNs code of conduct.
The precedent on this was really the Samaritans Purse incident where they went legal trying to get users details to go after them personally. That was nasty and very very scary for some of those involved. It's a subject that can't be freely discussed on MN even now because of the litigatious nature of the organisation.
Ultimately MN pride themselves on trying to stop this being a situation which may be repeated where users believe they are anonymous but are then pursued legally and MN have to effectively 'give them up' and a user might find they are less anonymous than they thought.
Not everyone likes the moderation on MN but I do get where it comes from and having seen the above incident, I think it's much needed.
You still need to be mindful of what you say here but I think it's better than the alternative for many who don't really understand the law and the limits of what you can say in writing.