IPv4, IPv6 and reliability

I didn't expect that this would be common enough to see it myself:

What it means is that IPv4 has become (or is becoming?) less reliable than IPv6 as a transport. The web service (a nice professionally run place) detects that my NAT gateway has tried to do something nasty, and blocks some functions from its IPv4 address. Thousands of people use that NAT gateway, because my ISP has more customers than IPv4 addresses and puts all of us behind one IPv4 NAT gateway.

IPv6 doesn't have this problem — each customer gets a unique IPv6 prefix so only the malevolent customer is blocked, the block won't affect thousands of bystanders.