That's GP's point. Service providers will block the IPs of abusive clients. If those clients are your cg-nat neighbours, you're blocked with them.

Try accessing the web through TOR and you see why public, shared IP addresses are quite a hassle in practice. Exit nodes don't host anything either, after all.

Actually, that's not even that bad a way to get IPv4 on any IPv6-only host: route it all through TOR!