Valuing "a relationship meeting criteria X" is not a belief, it's a term in a utility function. "People would be better off if their relationships had criteria X" is a belief that may or may not be justified. Determining the latter to be false in the general case does not invalidate the former.

Furthermore, your argument seems to be based on the observation "Most relationships do not meet criteria X" which is true but logically irrelevant to either of the above propositions.