I agree and disagree. I think the main point is, is the person who needs to vent your friend or not?

My friends can vent, whine and use me as an unpaid therapist any day. They have earned that right. But I have a well-curated, very short list of friends who can rely on me as much as I can rely on them. They care about me. They listen to my problems. We support each other.

With acquainces or friends-of-friends, it depends on how much I like them, but I will usually indulge them, say, the first one or two times. But after that I establish boundaries.

With a person like OP described, though, I would be very short. I have no patience for emotional leeches.