The best analogy seems to be trespass. A store generally allows anyone to come in. Absent any kind of notice you can go into a store and take pictures. But if there is a big prominent sign on the door that says "no photos allowed" and you go in and take a picture, you aren't just subject to being thrown out. You are (depending on some nuances of state law) committing criminal trespass. Likewise, if for whatever reason, you've already been thrown out and told you are never welcome back then the minute you step in the door you are trespassing.

I don't see any reason why e.g. a website that prominently displays a notice saying that scrapping tools aren't welcome and that puts in place reasonable measures to prevent scrapping tools from being used, shouldn't be protected by the law of trespass from people that deliberately evade these preferences. Likewise, I don't see a banned HN poster that creates a new account shouldn't be considered a trespasser. Of course there are issues of prosecutorial discretion and limited law enforcement resources, but that's a separate question than what should or shouldn't be criminal.