I don’t think that just about any behavior is fine (in the sense that it does not indicate a problem about the people involved), even if the people involved are consenting adults.
If one adult finds it pleasurable to be shat upon by a roomful of other adults, or finds it pleasurable to have their bones literally broken by others, then that person has a screw loose/is sick/is mentally ill (or whatever term you want to use)
I don’t care if something is listed in the DSM-IV or not. Behavior like the one mentioned above is sick. If it is claimed that even the above behavior is not sick, then the word will have lost any meaning.
Now, regarding the case mentioned in the OP, from the other thread, I don’t think we have enough info, but from the few things I have read in these two threads it seems to me that people who need to be dominated, who need to be told what to do, who enjoy being humiliated have a screw loose.
They may be functioning adults in every other sense, but not all is well in their head.
Like people with OCD: They may be functioning adults in every other respects, but when they go home they may need to wash their hands exactly 7 times and count all their socks before they can have dinner. They have a screw loose.
I’m not suggesting that we take any particular course of action. If they are functioning adults, let them do whatever they want. But to suggest that they are perfectly normal is wrong.
If this 24/7 D/s thing spills over into “real life” (e.g. ordering and humiliation in front of co-workers, extended family, friends, etc), I would find it to be quite disturbing/sad/sick. On the other hand, if it doesn’t spill over into real life, then it isn’t really “24/7”, is it?
I think she said that she calls him “Sir” in public, and she was made to wear some dog collar at a restaurant, but I don’t think enough details were given about how much this spills over into the other domains in her life to be able to say whether their particular arrangement is disturbing/sad/sick.
Finally, the attitude “I’m fine with the behavior, but I don’t want the kids to be damaged” is a bit inconsistent. If the behavior is fine, then, even if the kid grows up to a dom or a sub, they are not “damaged”, since you already mentioned you are fine with the behavior (if they grow up to have dom behavior with non-sub people, then that obviously would be a problem)