Fear of litigation - it pervades all of society - even this forum is crippled by it.
It's not so much the fear of litigation - it's that we really can't be bothered to have to defend ourselves over something that someone
else says on a discussion forum. Forum posts are, after all, not that important in the grand scheme of things - I'd rather spend my time (and money!) on something more constructive.
We are quite happy for other people to go and say what they like about whomever they like in their own backyards, but by posting it in ours, unfortunately (as publishers), we get dragged into any legal stoush - and we have very little interest in fighting other people's battles for them.
Our caution is about pragmatism really.
We do regularly tell people who threaten us with legal action (politely) where they can stick their threats (if we think they are baseless) ... but we also regularly remove content which we agree steps over the line, especially where it breaks our own rules. It's all swings and roundabouts.