I think that as long as people are happy with where they are, and what they're capable of doing, then it is not wrong. I could hardly care less if a couple is embarking on a career in tango escenario or just shuffling around the pista; if they aren't disturbing anyone and maintaining the flow of the dancefloor, then it's all good for me.
That said, I am a very strong proponent of the maxim that no one is obligated to dance with anyone.
I dislike the fact that many dancers think that being friendly means that they have to dance with someone, because that just greatly reduces the potential for developing friendships. If the prevailing attitude of (being friendly == must dance) would just go away, I think milongas would be more warm and social.
I dance with beginners, because I want to give back to the community, even though I don't usually derive the kind of enjoyment I want the most from dancing with them. And I hate that whenever I'm at a follower-heavy milonga, I have to endure stares from bad (for some definition of bad) dancers whenever I'm sitting out a tanda.