"except when you spend 2 hours in a conference explaining why people should use free software. At that point, as a service user, RMS says something about someone else's computer."

As to "spend[ing] 2 hours in a conference explaining why people should use free software": Be careful about the trap of concision as explained by Herman and Chomsky in "Manufacturing Consent". It takes time to lay out new ideas, ideas which mainstream media never discuss. Software freedom is still (even 30+ years after the fact) regarded as a new idea.

Regarding saying something about someone else's computer: I don't clearly understand your point. Are you sure this isn't giving someone convincing reasons to favor free software? Can you point to an example of where RMS is a service user and makes demands of that service beyond recommending what they ought to do to get the software freedom they deserve?

"I agree with the logic of your argument, but it sounds like a lawyer's argument : it's ok by the law eventhough i'ts not super "ethical"."

What's not ethical about not having control over someone else's computer?