The pushback against "slopification" is an ad hoc justification that is nebulous and vague enough for people to use to feel superior about their opinions and ideas, but has no genuine grounding.
But even if we consider the slopification argument, don't factories produce slop as well? Fast fashion is notorious for producing slop. But at the same time factories also produce are cars, shovels, housing, screws, etc. are they "slop"? How about computers? And other advanced manufacturing? Still slop?
Even if we consider the slopification argument, it isn't strong enough.
The use of AI to produce slop is a non-argument. On the same level of argument that an open internet would produce scams, proliferation of pornography, and gross commercialization/ads. All true, but still a lot of new value was unlocked from n order effects.