Causing unnecessary pain and suffering is not compatible with being humane. It's as simple as that. There are better solutions with fewer side effects for every use case of a shock collar. If not every single use case, the overwhelming majority of them. (edit: I didn't realize you were the one advocating using shock collars on a rescue dog that barks too much. A shock collar isn't even in the right ballpark in that case.)

Dominance and pain based training methods are outdated and based on debunked theories, in the past three decades almost the entire field of animal behavior has moved on.