First, as we are all aware, there are many people on the ‘net who have a rather loose grasp of reality (9/11 Truthers spring to mind here). Their arguments need to be countered but if you attract their ire you really do not want them knowing who you are.
Second, some bloggers make use of anonymity to blow the whistle on malpractice and corruption. Leaving themselves open to retribution could make people less inclined to speak out. Obviously, this could not possibly be the intention of the European Parliament but the consequence is there nevertheless.
Third, many bloggers (including myself) must avoid giving the impression that they speak for their employer. Hiding ones identity achieves this.
Fourth, Mikko appears to be under the impression thast one must know the identity of bloggers in order to evaluate what they say. This is the sort of sloppy thinking that Ben Goldacre criticizes in “Bad Science”. Surely, it is what is said that is important, not who says it? Would my posts on education in Britain become any more (or less) true if you knew my real name and where I work?
The way to decide whether bloggers are worth reading is to note what evidence they provide to back up their assertions and whether or not they link to original material so that you can check the facts for yourself.