Journalists, of course, owe their loyalty to the public. But that is far from an easy task. In the mix of a zillion forces all tugging at journalists for attention, ideals are lost. Performing the watchdog role is impossible this day in age because of the attitudes and practices of people. People tend to look at the media with an untrusting eye. While it's not a negative trait to have, many people refuse to trust anything and won't hear any proof otherwise.
This view towards the media can help spark an attitude of "us vs. them." When a situation such as that occurs, it's easy to shift loyalty. Journalists then looking to clean the collective opinion of the media may then go to extremes to make quick progress. In that case they still aren't being loyal to the public, they are being loyal to themselves. It's a double-edged sword.
PR practitioners owe their loyalty to whomever employs them. Their job isn't to inform the public and be fair, their job is to help bring in money.
I believe that loyalty is very important, but difficult to practice. Depending on the situation and who is involved, loyalties change and new enemies seem to be made.