Yes, this is a definition of an ISP. The ISP transmits requests from users to the internet, and the requested data back to the users. This is the product that Comcast already provides and charges their users for.

The users ask for internet content, the ISP (Comcast) is responsible for delivering it. If the users are clamoring for more content, taking more bandwidth, so be it. Comcast charges end users more money for more bandwidth already, through different pricing Tiers. If their infrastructure isn't big enough to keep up with customers demands then either they aren't meeting their existing contractual obligations with their customers, or they are falling behind technology wise. They have the money to keep up. They tend not to invest enough in their infrastructure, but that is a business issue. If Comcast is unhappy that users are using the service they paid for, they may need to restructure their offering to users, for example paying for bandwidth as a 'per amount transferred'. The critical point here is that it is a relationship only between the ISP (Comcast) and the end user, and the content providers aren't involved.

It is incredibly dangerous to confuse their relationship with their users with outside entities.

Net neutrality doesn't mean Comcast has to handle double the traffic from Netflix. Net neutrality means that Comcast has to handle the traffic from Netflix in the same way it handles it from other places. It could be slow, choppy, and a bad experience. They could choose to invest in a better network or not. They can charge users for more bandwidth, or other related infrastructure services.

What they cannot be allowed to do is discriminate against users and outside companies.