> [citation needed]

Nearly 85% of all emails are spam. source: https://dataprot.net/statistics/spam-statistics/

At times that number has been even higher with over 90% of all messages sent over the internet being spam. If 90% of all the messages in your inbox were spam how long would you continue to use it? Email systems can't bear the costs that spam forces on them. Even with tools like blacklisting which you think shouldn't exist that cost is measured in tens of billions annually. source: https://www.aeaweb.org/articles?id=10.1257/jep.26.3.87

If not for the ability to filter common sources of spam, email would never have survived as a viable means of communication.

> It's way more than 0.001%. Like, several orders of magnitude more.

Whatever the actual number, it's clearly acceptable to us because blocking irresponsible networks is standard practice. We depend on it.

> What overwhelming amounts of spa

Again, 80-90% of all mail is spam, costing billions. If you're able to run a mail system without blacklists that's great for you, but it clearly doesn't work for everyone.

> You don't get to decide what's acceptable to everyone else.

That's the beauty of the internet. I don't have the power to force an abusive network to do their job and prevent spam from leaving their network and that abusive network can't force me to accept mail from them. No one can force anyone to do anything. All we have is a loose set of standards and expectations and it's up to each network to decide what to accept or not based on how well those standards and expectations are followed.

> Any ISP that accepts significant numbers of customers will occasionally have a customer who is either malicious or operating with imperfect security allowing someone else who is malicious to exploit them.

A responsible ISP identifies those users and prevents them continuing to cause problems. If they refuse to do that their reputation suffers and they will get blocked. If they do their job too slowly or too poorly they will be blocked.
Is it possible for a responsible ISP to end up on blacklists? Yes, it is, and there are blacklists that don't maintain their lists well. That's fine too because no one is forced to use them. It's still the case that every network has the choice of what blacklists they will or won't use and how they use them. They can whitelist blacklisted IPs they decide to trust and they can use blacklists to greylist instead of block.

> The kind of policy you advocate punishes small ISPs just for being ISPs

Nope. Even small very ISPs can staff their internet abuse departments adequately and implement anti-spam technologies to prevent their IP space from becoming a safe haven for hackers and spammers. If they choose not to do that they will and should be blocked.

> I invite you to apply the same policy fairly and neutrally to larger organisations such as the major mail forwarding services and cloud hosts as well and see how long you survive in this industry.

I'll agree that there are problems when certain services (either cloud providers or mail providers like Gmail) become "too big to blacklist". We've had that problem with AOL and we have it now with Google. Personally, I'd prefer to hold them to the same standards as everyone else, but the problem of the largest players throwing their weight around giving them unfair advantages exists in every industry and until someone comes up with a solution for it, we're all just stuck playing along.

> Block actual spam sources

If your ISP is a safe haven for spammers and hackers their IP space is the spam source.

> provide a reasonable method for removing blocks that are no longer necessary.

So your alternative to blacklists is just more blacklists that are run better? I think everyone who depends on blacklists would like those blacklists to be better at detecting spam sources and better at clearing unnecessary listings. The good news is that badly run blacklists don't tend to get widely adopted because they cause more trouble for ISPs than they are worth.

If some network won't accept your mail and you're convinced that your ISP is acting responsibility and that it's the blacklist that's wrong, you can have the person you're trying to reach contact their ISP to get your mail server whitelisted. If an ISP sees that a blacklist they use is catching too many messages that it shouldn't they'll adjust their thresholds or stop using that list.

It's not a perfect system, but it's the best one we have.