It is an open protocol. What is so hard for people to understand that means in can be used against your cause?

There will be several custodial Nostr clients, it’s only a matter of time.
They may unfortunately be even be more popular than non-custodial someday. 

The key is to make the experience better on non-custodial apps than on the custodial apps. 

Email works better custodial, web hosting works better custodial, there is another chance to overcome those two issues and more with making Nostr better as non-custodial.

That will be possible when we acknowledge the serious user experience issues with non-custodial and work to constantly make the experience better than custodial.
ZBD solves many experience issues for its users and ignoring that is doing us a disservice.