To flood bots with gibberish that you "think" will harm their ability to function means you are in some ways complicit if those bots unintentionally cause harm in any small part due to your data poisoning.
I just don't see a scenario where doing what author is doing is permissible in my personal ethical framework.
Unauthorized access doesn't absolve me when I create the possiblity of transient harm.
I'm basically saying 2 wrongs don't make a right here.
Trying to harm their system which might transitively harm someone using their system is unethical from my viewpoint.
Most of these misbehaved crawlers are either cloud hosted (with tens of thousands of IPs), using residential proxies (with tens of thousands of IPs) or straight up using a botnet (again with tens of thousands of IPs). None respect robots.txt and precious few even provide an identifiable user-agent string.
Your chemicals in river analogy only works if there were also a giant company straight out of “The Lorax” siphoning off all of the water in the river.. and further, the chemicals would have to be harmless to humans but would cause the company’s machines to break down so they couldn’t make any more thneeds.
1. The machines won't "break", at best you slightly increase when they answer something with incorrect information.
2. People are starting to rely on that information, so when 'transformed" your harmless chemical are now potentially poison.
Knowing this is possible, it (again "to me") becomes highly un-ethical.