In some cases, there are features that would have a negative impact on security if nothing else is done. It may be desirable to adopt the features anyway, but in that case, the corrective action is mandatory. They are not, primarily, a response to network protocol security problems per se. Rather, they are a means to compensate for failings in software engineering and system administration. Anything that makes firewalls harder to deploy will make IPng less acceptable in the market.
Firewalls impose a number of requirements.
First, there must be a hierarchical address space. Many address-based filters use the structure of IPv4 addresses for access control decisions. Fortunately, this is a requirement for scalable routing as well. Routers, though, only need access to the destination address of the packet. Network-level firewalls often need to check both the source and destination address.