After Wisconsin finds out how to reliably filter vpn, they can then teach Netflix and Akamai how to do it. Last time I checked modestly reliable geoblocking existed, and completely unreliable vpn blocking. A friend told me that when he comes across a site for which Nordvpn is blocked, he just changes IP. Latest the third one always works, even on YouTube (he is all about privacy).
You don't have to reliably block something to make a law against it. Murder is illegal despite the government not figuring out how to reliably stop people from murdering each other.
However, to address your specific chosen example, one could argue a difference from murder, if they say “your site must block these traffic sources or you’re in trouble”: one could argue (it’s not at all cut and dried) that it’s like saying that venues are liable for the murders committed at them, rather than the murderer.