If host A is using gmail to spam me, then I can block host A, but if gmail would remove this I can only block all of gmail (or the gmail account, but a new account will be created 2 seconds later, whereas creating new IPs is much harder).

I'm all for privacy and prevention of leaking data such as IP addresses, but there are other concerns, as well, which I often see "privacy advocates" forget about. Maybe there is a better way to solve this problem than including the IP address – I would be all for it – but this post doesn't mention any of this.

Unfortunately, 100% privacy is often open to abuse from malicious actors, and a balance needs to be struck.

BTW: you can make a similar argument about the stamps the post office puts on your letters, which often includes the location and may be "private information".