We have two perspectives, the normal user and the scraper. The normal user either acquires a /64, /56 or /48, depending on the whim of their ISP. There is typically no cost difference between these options, which means that the scraper (or their upstream proxy) always chooses a provider which offers a /48.
Thus, the default unit of IPv6 blocking must be a /48. This situation will persist for as long as /48s are readily available at the same price as /64s.
Perversely, the reason we don't have this issue in IPv4 space is because the address space is of the same order of magnitude as the number of potential users. That artificial scarcity means that a routable /24 is x256 the cost of a end-user /32, so the unit of blocking can be a /32.
> Perversely, the reason we don't have this issue in IPv4 space is because the address space is of the same order of magnitude as the number of potential users.
Do we not? And is it really?
There are some /32 IPv4 addresses hosting many users, e.g. with CG-NAT, and it's already an issue with regards to blocking/rate-limiting.
Just like there are single-user /48s and multi-user /64s, there can be single-user /32s and /32s hosting tons of users behind a CG-NAT.
Sure, but that's the same argument I'm making: the unit of blocking will be the largest unit that is routinely allocated to a single user. In IPv4 space that's a /32, so people block by /32. In IPv6 space that's a /48, so people block by /48. Check out Let's Encrypt's rate limit policy, for example.
The difference I'm pointing out between IPv4 and IPv6 is that nobody is giving single IPv4 users /24s for their own use. But IPv6 /48s (which are theoretically somewhat equivalent to IPv4 /24s) are freely available. This is a problem because it makes over-blocking even more likely than it already is. And as you point out elsewhere, over-blocking is already an issue in IPv4 space.
Thus, the default unit of IPv6 blocking must be a /48. This situation will persist for as long as /48s are readily available at the same price as /64s.
Perversely, the reason we don't have this issue in IPv4 space is because the address space is of the same order of magnitude as the number of potential users. That artificial scarcity means that a routable /24 is x256 the cost of a end-user /32, so the unit of blocking can be a /32.