If your browser doesn't play nicely and obey robots.txt when its headless I don't think it's that crazy to block the browser and not the user.
It's the user's responsibility to behave well, like in life :)
Banning the root library (even if you could with UA spoofing and whatnot) is right up there with banning Chrome to keep out low-wage scraping centers and their armies of employees. It's not even a little effective also risks significant collateral damage.
It's also trivial to detect spoofed user agents via fingerprinting. The best defense against scrapers is done in layers, with user-agent name block as the bare minimum.