I think Apple Pay includes the bare minimum friction to determine that you actually want to spend your money. I don’t think any less friction is ethical. I assume the Google program uses a cookie or similar technical means to indicate your membership in the program, which you previously opted-in to paying for through a flow with affirmative consent. That seems like an appropriate solution, and it shows that this model is supported by current browser tech. Websites are free to create their own membership programs, or band together and form cooperative programs, devising any system they like to set prices and divide up the revenues.