IANAL, and I'm German, not American, so I can't speak to the legal situation in the US.
But in Germany, the section of the copyright law concerning data mining specifically says that scraping websites is legal unless the owner of the website objects in a machine-readable form. robots.txt very clearly fulfils this standard. If any bot owner complains that you labelled them as a bot as outlined above, they would be admitting that they willfully ignored your robots.txt, and that appears to me to make them civilly liable for copyright infringement.
I also had a look if these actions would count as self-defense against computer espionage under the criminal code, but the relevant section only outlaws gaining access to data not intended for oneself which is "specifically protected against unauthorized access". I don't think this claim will fly for a public website.
But in Germany, the section of the copyright law concerning data mining specifically says that scraping websites is legal unless the owner of the website objects in a machine-readable form. robots.txt very clearly fulfils this standard. If any bot owner complains that you labelled them as a bot as outlined above, they would be admitting that they willfully ignored your robots.txt, and that appears to me to make them civilly liable for copyright infringement.
Source: https://www.gesetze-im-internet.de/urhg/__44b.html
I also had a look if these actions would count as self-defense against computer espionage under the criminal code, but the relevant section only outlaws gaining access to data not intended for oneself which is "specifically protected against unauthorized access". I don't think this claim will fly for a public website.
Source: https://www.gesetze-im-internet.de/stgb/__202a.html