Oh no! I believe it’s a legitimate concern - many parts of the world don’t have loads of IP addresses, and it’s much more common to see them pooled than it used to be.
Hmm, I don’t think that is any assurance of not disenfranchising lots of people.
I think the idea of blocking the IP address of a spammer is a tactic which comes from the USA and the times of individual bad actors and home access from cable-provided internet. I believe it’s quite inappropriate now.
It can be helpful to check an IP address against a well-maintained stoplist, or to check the address’ ASN against a stoplist of unlikely sources (cloud providers, for example). It’s still not great to block on that basis, if you want to allow people to sign up using VPNs.