Of course there are possible mechanisms. There are heuristics to detect bots. The whole reason for this lawsuit is that LinkedIn blocked hiQ from scraping their website.
I'm also not necessarily talking about a technical defense against unwanted scraping. Write a law makes it illegal to do something like "scraping personally identifiable information and storing or presenting it non–anonymized", and prosecute companies who break it. I'm sure there are loopholes in that particular example, but the point is we can absolutely add shades of gray here.
> Open for everyone but those whose applications you don't like isn't open.
Openness should be a means, not an end. If we make something "not open" but it prevents 95% of undesirable uses and only 5% of desirable ones, is that not a tradeoff worth discussing?