It hurts more than just Chargify and their customers, it hurts anyone running such a service as people will be more likely to avoid services that they can't trust to keep their pricing stable (or at least give plenty of advance notice, 6 months to a year).
These kind of changes definitely make me think much harder about outsourcing a service. How can we trust the current pricing? Do we have to change our pricing every time they change theirs? How many customers do we lose based on their bad business decisions?
Chargify knows that people have spent time integrating with their service. They hope that this will give them a percentage of paying customers, knowing full well that they will lose a lot of customers. This is definitely a bad move for Chargify and a good decision for their competitors.