If I have a terms of service for my SaaS where I've snuck in a vague term that I can "charge additional usage fees at my discretion", it doesn't mean I get to actually charge you $100,000 because I found out your favorite color is blue.

There's absolutely an expectation of reasonability and good faith.

Nobody signing up for Claude would be reasonably assuming that they are allowed to arbitrarily decide what magic words suddenly bypass the subscription cost model that was actually purchased into an overcharge model that is significantly more expensive, whose verbiage clearly indicates the intent of the feature being enabled is to allow additional use after the quota has been consumed, not randomly at the behest of Anthropic.