I've ridden thousands of miles on department store bikes and still have two of them that I ride regularly today, (I rode 35 miles yesterday on an old Costco Mongoose).
Their biggest problem for a serious cyclist isn't that they don't work properly or are "bike shaped objects", but rather that they are a cut rate product. If you're a regular cyclist for a year or more, chances are you'll end up with at least one pretty nice bike. If you've been riding for 5 years or more, you'll almost certainly have at least two nice bikes, and more likely half a dozen. What's more, the bikes you own probably fit YOU correctly, rather than the average teenager. You've probably tuned your bikes pretty darn well. When a brake squeals, you replace or adjust the pads or if it's ghost shifting, you find out why. You keep your bikes indoors, or at least under cover. Finally, you've got a few bikes you've been lusting after and they're all either high end or rare.
For a person like that, a heavy, one size fits all bike with low, low end components and many obsolete parts, that's been poorly assembled, improperly adjusted and likely neglected really does seem like a complete turd. Even if it works perfectly well, why would you bother riding it when there are so many nicer bikes out there?