P2P protocols don't have much problem opening up a stateful firewall connection as you just have to send one packet out to open a known address and port.

I prefer to run scrapers behind CGNAT because websites can't ban it without causing collateral damage, which matters more to some than to others. The website probably has to put up a captcha. Which hurts its human traffic. Think about how much more traffic you could have if you didn't show everyone a captcha, and you might see that you should also be in favour of IPv6.

> 1) my stateful firewall is going to break most of that anyway

Your CPE is probably running UPnP IGD and/or PCP for hole punching of P2P services, and IGD/PCP can hole punch just as easily for IPv6.

> 2) if cg nat is as popular as people claim then they won’t be doing that as it’s not an edge case

It's not whether CG-NAT is an edge case or not, it's whether there are things that are completely impossible with it or not. Want to play with your friends on your Xbox/PS? Too bad, CG-NAT makes it completely impossible.

Why should we be happy with a technology that makes certain use cases impossible? On what planet is that a good thing?

> 1) my stateful firewall is going to break most of that anyway

Stateful firewalls and even regular NAT aren't much of an issue for P2P, but CGNAT is much more problematic [0].

> 2) if cg nat is as popular as people claim then they won’t be doing that as it’s not an edge case

You'd hope, but people tend to be pretty slow to update their networking assumptions, so this is still pretty common. And it doesn't help that most CGNAT users tend to be either from poorer, since poorer countries and mobile data providers are far more likely to use CGNAT than legacy North American ISPs.

[0]: https://tailscale.com/blog/how-nat-traversal-works