OP, I think it might have been more helpful to frame your post less as "the problem with Goodreads is that it makes reading an achievement" and more as "tracking my reading turned it into a chore" (or however you want to qualify your experience).

Then people would be talking about their opinions on reading tracking, gamification, and motivation (which is what I think you were trying to discuss), instead of specifically why Goodreads is good or bad. Shame that's what people latched on to.