I think a lot of really smart people are letting themselves get taken for a ride by the web scraping thing. Unless the bot activity is legitimately hammering your site and causing issues (not saying this isn't happening in some cases), then this mostly amounts to an ideological game of capture the flag. The difference being that you'll never find their flag. The only thing you win by playing is lost time.
The best way to mitigate the load from diffuse, unidentifiable, grey area participants is to have a fast and well engineered web product. This is good news, because your actual human customers would really enjoy this too.
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