This seems like a very good reason to have a law about it: if the only reason you log IP addresses is that it's on by default and you haven't thought about the risks of storing it, you should think about it for your production servers. Otherwise it's purely a risk and has no benefit. (And the risk is to your users, not you, so it makes sense that a law would be needed to give your users the ability to complain about that needless risk.)
If you make the active decision that you specifically want the IP addresses, great, you can do that. Just have a strategy for keeping that sensitive data secure and getting rid of it at some point.
It's not a phone number because it doesn't need to resolve back to anything in particular. With carrier grade nat for instance, it could be shared by many people. At best it's shared by a house.
With regards of tracking you with the help of the ISP, if you have someone with those resources, it's not you storing an IP address that's their biggest concern.
Geoinformation can also change daily. Figuring it out afterwards isn't reliable.
If you make the active decision that you specifically want the IP addresses, great, you can do that. Just have a strategy for keeping that sensitive data secure and getting rid of it at some point.