Open collaborative design/Isn't this design by committee?

It has been said that a camel is a horse designed by committee... Won't this development model just create a herd of camels?

Not at all, because there is no single 'conclusion' that a design must arrive at (unlike a committee's decision). As with software, it might be that an original design is created by a single motivated individual, or a small group of people with a common purpose and shared vision, but beyond that the design can be evolved in multiple directions by other interested parties who might need a particular variation.

Many fine horses have been created within the open-source software world and it will be the same with design and engineering.