Not true. When you remove net neutrality, you open up new possibilities for price-discrimination for the monopolist and they can extract more revenue for providing the same service.
Simple illustrative example: Suppose for the sake of argument that almost all VPN users are willing to pay an extra $1 / month for VPN access. Then Comcast can make strictly more money by charging everyone exactly the same as before except VPN access costs an additional $1/month.
(Also, I know you didn't bring it up, but there are lots of important free speech NN issues as well as economic ones, for example, Comcast might easily decide to completely block sites like Wikileaks.)