I've thought a lot about this question over the years. It's a question that comes up quite often concerning musical instruments, but I think you can apply the logic behind it to just about any handmade item.
We always hear about how handmade means better quality, as though several people working on an a guitar (for instance) cannot possibly produce something on the same quality level as what one person working on his own can produce. I guess the logic behind this says that one person working on his or her own, and not under the supervision of a company, nor the constraints of a time-clock, will be able to take the time to do a job right. And for some reason, the people who perpetuate this viewpoint seem to take it almost for granted that a person working solo will be wonderfully gifted and be able to work magic into their creations. Thus, they can charge top dollar for them too. I say hooey!
Since I know a little about guitars I'll take those as my example. I've personally come across many poor sounding, and poorly crafted, handmade guitars with glue drips hanging on the inside and imperfections in the finish on the outside, not to mention poorly executed joints and worse. I've also seen my fair share of people running all kinds of small businesses who work alone and do shoddy work from accountants to house painters. Working solo never made anyone a magician.
Big musical instrument manufacturers can, and often do, make instruments that not only rival, but may surpass, handmade instruments, and do it for a third of the price. Think about this a moment. A luthier building acoustic guitars on his own can only produce six to ten guitars per year on average according to most I've seen interviewed. Some will take on one apprentice, maybe a son, and double production. (People still tend to think of this as handmade though.) Any of them will tell you that it takes a long time to get good at it. Just learning to apply a finish properly takes nearly a year of experience. But these guys have to do it all—everything from carving out curved bridges to doing fretboard inlays and scalloping internal braces. How good could you possibly get at doing everything that goes into the crafting of a guitar, or much of anything else, if you only do a half dozen of them in a year's time?
On the other hand, mass produced instruments are made by people who typically specialize in some aspect of their job. One guy may do nothing but make bridges all day, every day, year in and year out. Another guy may do nothing but make tops. Let's say both of these guys make six per day, five days per week, and have been doing this for five years each. That's roughly 6,500 bridges and tops in five years. Wouldn't you think they'd be incredibly good at making bridges and tops compared to someone who only makes six of each in five years time? Further, workmen who are well-supervised are forced to do good work. But a guy working on his own may do shoddy work in any given area and not think twice about it since he answers to no one.
In my estimation, a product that comes from a well-supervised production line by experienced workmen should generally be higher quality—not worse. Just seems like good horse sense to me.