If it allows paid fast lanes, then clearly it allows degradation.
That is objectively false. Degrading the "slow" lanes is only one way to produce a fast lane. Direct peering arrangements and co-location of services are two ways to create "fast" lanes without having to degrade anything. They are also not free, so it makes sense that business-to-business deals would be made to establish them (aka paid fast lanes). The effective bandwidth of the internet looks like an hour glass. As…
It doesn't have to be "actively" slowing down traffic to be degraded. If ISPs can go faster, and they choose not to unless you pay more, that is a form of degradation. One of many forms the degradation could come in is ISPs failing to build out faster networks until people are paying higher prices. Service can be allowed to degrade over time by simply not doing anything unless you pay more money.