Unless you think UFAI is a problem so large that all others are irrelevant, there's room for people to work on other problems justifiably.
See this article. At any given time there's likely only one maximally efficient use of your time/energy/money resources on the margin. "Justifiable" sure (I don't know what that word means), but don't call it utility maximization.
http://esr.ibiblio.org/?p=6549