I do agree with Sir William. However, there are many exceptions to most rules. It is all situational. There are a lot of imaginable situations in which an un-practice amateur's poor performance can have a direct effect on another professional's working environment, but as a general rule of thumb, I like the original blog's post stating that a professional should always just aim higher and try not to dwell on what could be potentially angering.
If there is a professional wedding photographer in a certain area, but a less seasoned amateur gets his name out there and manages to steal away some gigs, because the client is also unaware, that directly takes revenue away from the professional. True, the amateur's reputation as an inadequate photographer will eventually surface, the damage for that one situation has already been done.
But again, it is all situational, could be big and could be small. In terms of magic, I do like the idea that Professionals should continue to just aim higher, boost their reputation and skills, to the point where the lingering amateurs have no other option but to respect the said professional and strive to reach his or her level.