edit I guess I've been shadow banned for wrong think in here, can't respond to comments.
Some states criminalize possession of substances others don't. Some criminalize certain behaviors and practices that others don't. Why should that stop at the freeways?
At least in the history book I used there is a direct parallel: a precedent setting case had to do with regulations about tractor trailer wheel mudflap sizes. States would set different conflicting values so that they could restrict the traffic through them (or force a waste of time before coming in).
There may also be another argument based on how states must, in general, respect each other's licenses (marriage, driver, etc; but interestingly not concealed carry, something I suspect will be tested again soon).
Right, but in our scenario they're not prohibiting them, they're prohibiting registering them. That's different than the mud-flaps issue, which does actually seem problematic in my opinion for exactly that reason: it inhibits inter-state commerce.
Keeping your post visible while disabling replies is the exact opposite of what shadow banning is.