From what I get out of the blurb on the linked page, reddit's only asking a given person to donate the kind of work that he does professionally. Which would act

From what I get out of the blurb on the linked page, reddit's only asking a given person to donate the kind of work that he does professionally. Which would actually make this a rare instance of volunteer work where your point doesn't apply in any case. Even if they're also asking for hobbyists, your point still might not apply, because people take pleasure in their hobbies -- and it's possible that value(output of x hours of hobby work + pleasure gained from x hours of engaging in hobby) > value(output of x hours of maximally efficient work).