I should think you are quite safe as long as you don't defame innocent people - are you able to post without doing so?
Tell me, are admin here experts on defamation law or are they just going to report things willy nilly on the off chance it may be libellous ?
If a person backs up a claim with evidence for that claim then it is probably not libellous.
The problem comes when people make claims (in this case, about the McCanns) without posting any evidence to back up those claims. Those claims could be potential libel and if in the considered opinion (I very much doubt any report would simply be willy nilly as you claim.) of moderators they appear to be so, reported as such. It would be up to others then to determine whether it is actual libel.
There are occasions where the claims made are clearly untrue and are actually contradicted by evidence which is easily available. Those could be reported as probable libel.
Personally, as I have no intention of libeling anyone and at all times endeavour only to post evidenced claims and I won't be abusing anyone on the forum then I won't be worrying at all.
I suspect people would only worry if they thought that what they were doing was likely to be considered abusive.
I know that there are many people on Twitter, for example, who post abusively there because they think it is unregulated and they find the thrill of being abusive quite intoxicating. Thankfully, I don't find I need that kind of thrill. I find life is perfectly satisfying without having to be so offensive.
Personally, when I see abuse happening I don't turn a blind eye. I do whatever I can to ensure that it stops. I think that is the decent thing to do. Those who either abuse others or even those who simply condone such abuse (for example, by criticising others who report their concerns) are in my view beneath contempt.