That's still not acceptable in 2019 last I checked. Hell, nearly nothing in Pink Flamingos wouldn't be shocking today, though much of it (like rape or animal cruelty) hasn't aged well.
But you've seen two girls one cup. You've seen people dress in fursuits and fuck, and been fisted, and sounded, and it may not be attractive to you but it's not shocking. That's what he's talking about.
I'm guessing that a minority of people on HN haven't seen video of someone dying in a gruesome manner. Perhaps it was ISIS sawing off someone's head. Perhaps it was someone falling from the twin towers. Perhaps it was somebody murdering a homeless man for fun.
It's not shocking. It's despicable, but it's not shocking.
Nazism and white supremacy and racism and misogyny isn't shocking - it's dismaying, but it's not shocking. It may be socially acceptable, but it's not shocking. If anything, it's hackneyed.
What is this radical art? Maybe 4chan shocked people a decade ago, but goatse/gap3 pranks preceded that, at least in my world.