I understand the point about the official, narrow definition of a service dog. Also, I don't dispute that many people claim service dogs that don't meet that definition.
But that feels like the debate about Illegal Immigrants. One side says "what part of illegal don't you understand" and the other responds with "hey, these are good humans."
I think that if a human says their dog provides a service, that the discussion stops there. The more you attempt to push back, the more people will explicitly circumvent it.
And really -- is this a major problem?