Been brewing on this for a few months so please excuse the fact that the article references below are a little old, inspired by yet another wave of 'death of journalism articles.'
Let's admit it- the reason that you see a lot of these columns is because of self-interest. The writers left standing in publications want to defend not just their peers but also their profession and their job. The debate then is whether this is really warranted or not otherwise. One argument against scribes is that the egalitarian nature of the Net levels the playing field and lets the masses storm the gate of opinion, making it more public again. Then again, just because someone has an opinion doesn't mean that they can express it well or as the old saying goes "Opinions are like assholes- everybody's got one."
There IS good reason to worry though as recently (well, relatively recently), the L.A. Times has cut more writers loose, including Chuck Philips (who admittedly had some big problems with sources to a recent story).
In my mind, a good music critic can serve two important purposes: 1) helping you to find out good music and/or 2) helping to think about music and issues around it. Admittedly, there's much more call for the former than the later and even then, there's a lot of competition from other sources, mostly online.
And that's where the big stink happens when professional writers complain about the Net, as for instance in this Guardian article. What they're worried about is whether blogging will or can (or should) replace print criticism, but maybe this a false set-up. Posting a link to a story or an MP3 file or an embedded music video isn't the same thing as writing a think piece or a carefully researched article- that doesn't usually happen in blogs and maybe it's expecting too much of them to think that they (always) should. Posting info can be a valuable service which you can learn something from- a good music blog can just as well help you find good music. To say that it's not 'journalism' per se is right but that doesn't take away it's value as providing a public service.
In the next installment (hopefully soon), we'll hash through some fallacies about the 'anyone can write' argument...