[SudoNick]

Lets ask the other question too: why do I not want IPv6?

It seems to me that NAT serves a very useful role in terms of helping to hide information about your internal network (the devices on that network, their roles and activity, etc).

I'm not well versed in IPv6 address assignment or Comcast's setup, but IIRC there are scenarios (SLAAC?) where IPv6 IP Addresses include an Interface Identifier that is derived from the manufacturer assigned hardware address. Which would allow a device's activity to be tracked over time and across the different networks it connects to. Which can reveal information about the type of device and potential vulnerabilities (to those who have access to the hardware address assignment database). Which can even reveal information about who purchased the device (to those who have access to purchase records that contain the device's hardware address).