I know. All the more reason to do it, right? If an ISP can't keep its network clean, then allowing them to send traffic onto the web is just asking for the problem to continue

Show people a useful error, such as "You are using [ISP name] which sends large volumes of abusive traffic (think of spam and DDoS). They allow the attackers to hop around points across their entire network so we cannot block the abusers more selectively. Despite our attempts to contact them, the abuse continues in volumes which we do not see from other ISPs. To access our corner of the internet, use a different ISP. You could try mobile data instead of Wi-Fi or vice versa.", and they can make their own choices about staying with this ISP if more and more websites show this sort of error

If everyone tries to identify people piecemeal, we all need to implement ~200 different identification systems (assuming each country has a central system that everyone is signed up to in the first place), or rely on algorithms to tell who is a bot (I'm currently being misidentified on a daily basis and I'm, eh, not a bot. Trying to buy public transport tickets is currently difficult, for example, because the monopolist in my country blocks me after a few route queries when using a Google browser, and 0 queries from Firefox)