Of course! Everyone complains. But that article isn't talking about general complaining or someone who is revisiting the same subject over and over until they can internalise and understanding of it.

It's talking about the people who are making no progress, no attempt to progress, that are not ready to make changes. Or people who are having great difficulty with being isolated by people in their lives because of their chronic complaining. Isn't it the duty of the therapist to point out negative behaviours that could be hindering that client from leading a happy life?

That article is not talking about discriminating or being cruel to these clients but offering "tough-love" offering to help them learn how to get to the source of the complaining, what's beneath the complaint, what's making them stuck.