Yes you want more users not less. This is business 101. Even business 000. Customers good.

Business 101 is to make sales! Users sometimes represent sales, but not always. That maybe Business 201 though.

This is about market share of a nonprofit - it's users.

Precisely their point: users don’t necessarily mean sales, but they MIGHT bring in donors.

Business 102, something that's obvious to anyone who's ever worked a customer facing job but incredibly elusive to a lot of people who went straight to management, is that some customers are net negatives and you should not cater to them. They have some combination of ignorance, stupidity, and/or malice which results in them costing more employee time and/or "goodwill" than you'll ever make from selling things. Your business is better off not having them, and even better if they go off to inflict themselves on your competition.