Zak S wrote a post about professionalism. I was going to use it as a springboard to launch into some horrendously pretentious rant about Alistair MacIntyre and Aristotle, but I'll spare you that. Instead, I'll just say this:
Professional ethics are important - or, perhaps it is more accurate to say that professional ethics were once actually thought of as being very important but are now often only nominally important in my professions. Professional ethics are the kind of thing that would once, in a (likely non-existent golden age) have prevented your local bank manager from granting you a loan because he was worried it might not be good for your long-term financial health; or which still prevent doctors from acting against the best interests of their patients or teachers against the best interests of their students. They tend still to be alive in the kind of professions which actually think of themselves as professions - doctors, accountants, lawyers (don't laugh), teachers, actuaries, whatever - but even there they probably have been somewhat eroded. There is some suggestion that this may be because we have become very tick-boxy and superficial about what "ethics" means, and this has resulted in a sense of what is called "ethical fading" in the literature: a tendency among people to see ethics as something that is mostly about process and fulfilling requirements and consequently not to consider whether their actual behaviour is ethical. Form over content, in other words - as long as you are doing the correct procedure that must QED mean you are behaving ethically (even if you actually aren't).
Professional ethics also seem to me to be tied to something we often call "professional pride" - the idea that you have a job to do and that it is important to do it well, for the sake of one's own self respect and for the sake of the image of the profession as a whole. The ideal marriage of professional ethics and professional pride is, let's say, a civil servant who refuses to cut corners not just because it is "the wrong thing to do" but also because it may have negative consequences for the public and for him- or herself; and because he or she actually cares about how the public perceives civil servants.
Anybody who has a profession (and a conscience) probably recognises that there are such things as professional ethics and professional pride and that they matter. Professionalism isn't the same thing as commercialism, for this reason. Commercialism is about making money. Professionalism is about doing a job properly. Everybody also probably recognises that the world works at its best when people who have jobs to do perform them in a professional manner (i.e. with professional pride and a sense of professional ethics).
So while I take the point that the spirit of amateurism (of doing something out of love) is very important in being a DIY RPG designer, I also think that a heavy dose of professional ethics and professional pride are by no means bad things. God knows there are enough failed Kickstarters, unpaid freelancers, doomed projects and pieces of shoddy rubbish out there to suggest that being a good DIY RPG designer means having the right mix of amateurism and professional ethics and professional pride. I by no means having anything like the right mix: I am as lazy, feckless and unethical as they come. But that doesn't mean I can't at least try.