I guess the first alternative seems like the more sane one to me, as far as legality goes. Website-crawling policies don't seem like the kind of thing that rises to the level where it's worth involving courts and laws, so I'd leave it to technological mechanisms plus voluntary compliance with non-technological mechanisms. But I suppose I have a pretty high bar for what problems are severe enough to require a government solution.

And pragmatically, the vast majority of the non-robots.txt-respecting crawls I see are coming from countries that won't enforce such laws anyway, so enforcing them in western countries seems like a downside (more entanglement between the internet and various countries' national laws) with little upside (won't stop many crawls).