> They never come from Google, and the bad programmed ones just crawl several pages at a time, faster than a user could do.

I’ve triggered this kind of “bot protection” right here on Hacker News many times. I did that by having a bunch of Hacker News pages open and then closing and reopening my browser. I’ve also triggered it by opening a bunch of links in the background too quickly. I’ve also triggered it by reading the article, then clicking back and upvoting/favouriting too quickly. I’m also located in Singapore, which people have started to advocate for blocking here recently.

A single non-bot legitimate user can easily trigger these kinds of heuristics just by using the site in a way you don’t expect. This can affect some users disproportionately more than others, e.g. disabled people who need to use assistive technology.