I'm going to take a little bit of exception to that notion. It's a simple fact that not all of the bargain-basement ammo is bad. In fact, some is quite exceptional. For many years, one of my favorite ammo choices (when I can get it) is plain old blue-box Federal. I don't see where you can find shootable ammo that is cheaper than that (typically about $17/box for 30-06 at Wallyworld). Yet, it shoots accurately and cleanly.
My only complaint with it is that they only produce it in certain calibers (most of which I don't shoot at all anymore or very seldom). I wish they would expand the line to include more calibers.
Nearly all of us can find some exception to the rule.
I, for example, consider Remington Express Core-Lokt factory ammo to be the benchmark for rifles chambered for .270 Win (130 gr) and .243 Win (100 gr - the
only 100 gr bullet I shoot in .243).
However, I think we can also (nearly) all agree that the cheap ammunition is, as an overal category, low quality.
...Which is why I hate any ammunition loaded with Winchester bullets, and why I refuse to buy any rifle ammunition from Federal.
Winchester Power Points, in particular, are the lowest quality, least consistent, most incredibly unpredictable bullet that I've ever seen. And then they stick it on top of an equally low quality powder charge.
Federal, I avoid because their factory loads tend to stretch primer pockets (thus, the brass is trashed) and I have had far too many DANGEROUS head space conditions presented with their lack of quality control. --And that's not limited to the cheap ammo - I had a $65 box of ammo with ONE HUNDRED THIRTY THOUSANDTHS of an inch (0.130") excessive head space; and in another box, cases that were eighty thousandths too long (0.080" - and unusable). Considering that most rifles have min-to-max headspace measurements of about 0.008" ... Federal only missed the mark SIXTEEN times, and ten times the tolerance. And that wasn't the only box of Federal ammo that I have come across with 0.130" excessive headspace.