Can't you say that about any profession, especially other forms of middlemen? Does it really matter if your grocer's motivation is having a nice house and good schools for his kids vs. feeding people and providing a market for farmers?
Yes. A grocer with illicit intent can poison the food that they serve because some God told them to do it. We need to ensure that they both are sane and correctly motivated. This isn't simply about providing welfare for people; it also concerns the identification of malicious intent and the avoidance of harm. There may be a few professions where this doesn't matter, but by and large I'd say an individuals motivation for choosing a profession does really matter (especially with middlemen).