Blocking 0.0.0.0 makes no sense. In IPv4 it is never routed.
What does "routing" a IP address mean?
Why is it the reason that blocking 0.0.0.0 does not make sense?
"Routing" means forwarding a packet based on its network-layer destination address, usually IPv4 or IPv6.
Routing is done by comparing the destination address to the entries in the local routing table and using the best (=longest prefix) match. The entry contains the next-hop gateway or the interface that the packet is then sent to/out of.
0.0.0.0/0 is the default route - because the prefix has zero length it matches any address. However, it is only selected when no other routing entry matches.
As IP address,
0.0.0.0 generally cannot be used (except as source address when configuring an interface, such as with DHCP).