Customers pay money for goods and services. They thus get a bunch of social, ethical, and legal positions in terms of their relationship with the seller.
Rsync is an open source project that its maintainers put onto the Internet. People who use it are not customers, and they do not have the right to expectations around how the maintainers will change the software or change how they develop it.
Customers are customers. Whether they're paying or not. Not all customers are worth servicing (even with infinite money offered, "firing a customer" is important to keep the community in check).
But this isn't a situation where the RSYNC maintainer should fire the customer. There's a LOT of backlash to this release. Even if this one particular customer is a bit of an ass, there's plenty of good users in that 90+ comment chain (hundreds now?) where this regression has clearly struck a nerve.
It was better when a dedicated PM was shielding me from this crap but here we are. Deciding who and who not to listen to is just part of project management.