From a Professional Philosophical point of view,
there is a distinction between statements of opinion and statements of fact. Statements of opinion propose (but, unlike arguments, do not seek to demonstrate) interpretations for facts. For example, an opinion would be, "I like the colour green". (A demonstration would be: when shown photographs of 40 pretty women, each with her eyes colored blue, green and brown, the synapses in the section of my brain associated with pleasure were 200% more active when presented with green eyes. Therefore I like the color green).
A statement of fact makes a claim about external reality. "Yesterday, there was a sea battle".
As pointed out earlier, allegations of fact also have legal significance. This is particularly true in a board like this one which is purportedly by and for professionals, yet anonymous and available to all (Welcome to one of the problems of the internet).
So take safety. A favorite jab against low-cost carriers is that they skimp on safety: or rather, management pressure on cost-savings initiatives often induces other parts of the company to take measures that are detrimental to safety. Is it justified? Sometimes it is and sometimes it isn't.
Making matters worse, there are conspiracy nuts and company axegrinders who routinely post negative material against particular companies, airports, and agencies.
But while this may be a "bull session" for pilots, it is, at least till now, a forum open to all, and occasionally cited explicitly in the press. People are reading these discussions and formulating opinions about who to fly with. Most of the time, you can assume that readers are critical: they know unsubstantiated BS and bitter employees when they see them. But if they get facts -- well, that's watercooler material tomorrow. And for Low Cost Carriers, since Valujet, if not long before, the public has been fed the suspicion that low prices=substandard safety. The most dangerous lies are the lies that support commonly-held beliefs; and, incidentally, the verisimilar is the biggest enemy of the truth.
So any statement claiming a factual incident where a given flight from a given airline busts safety regulations on a given day is going to attract attention. And you can bitch about Ryanair's counter-allegations all you want, but while there's an investigation in process that will determine the facts -- in a legal sense at least -- there's no reason to make statements of fact about the situation without indicating sources.