Hello, thanks for asking this question! This is a bit of a subjective one, but I’d say as long as the service dog is well taken care of, loved, and has enough time in between helping their person to be a dog and have some fun, then I do not consider it to be exploitation.
Where the waters begin to become a bit more murky is when we look at police animals, which are often seen as workers before they’re seen as animals. The police dog situation seems more unethical and exploitative than someone who needs a dog to guide them or be with them when their mental health issues flare up.
Expecting a dog to sniff out drugs in an airport all day is different (to me) than expecting them to take the lead and protect their person on a walk or provide support (largely in the form of cuddles, love, and fetching prescriptions from the other room) when needed.
It’s that fine line between a pet that also serves a purpose and and animal that is solely being used for its natural and trained abilities. Overall though, its all about the care they’re getting, and that goes for all animals.