Crates are too hard and pointy to safely land on, and our natural impulse to jump clear is stymied with nothing to laterally push off of.
BTW Costco started selling foldable crates. They are nowhere near as strong as milk crates but they stack well up to human height and there is a certain satisfaction in not possessing stolen property.
My take on this is that possessing a milk crate does not even rise to the level of Grand Theft.
It’s like people getting hopped up and armed about “illegals” in the country, when overstaying your visa or crossing outside of a border checkpoint is a simple misdemeanor.
It’s not all that hard. You just need to buy them where businesses buy them. Both Uline and Grainger sell them online and some restaurant supply stores carry them.
Get yourself to a salvage yard. The odd vintage one will show up at charity/used shops as well. I think I’ve probably got a dozen or so legally obtained milk crates on the property right now, all from either of those two sources. Most are the durable, non bendy plastic, but we have a few of the old wire dairy gold crates too.
If you don’t want to search, or need a matching set, the container store frequently stocks a modern copy with the right dimensions and look but with none of the banged up charm. Still does the trick if you need a legally obtained milk crate in a pinch.