If Interstellar were a religious text, the dogma it encodes could be called something like “scientific romanticism.” This belief system would hold that science will solve all of our problems one day, even the ones that by definition resist empirical observation and thus exist outside the purview of science (see Sagan’s Contact for another dogmatic specimen). Scientific romanticism works well as a narratival contrivance, but when employed to spice up the lives atheists who otherwise think that they have a clearer-headed view of the universe than those troglodytic believers, it can expose the scarcity of meaning available to those who eschew belief in God.
Love’s value is apparently utilitarian, not ontological. It serves a purpose, but it has no value by itself. In these terms, the self-love of Dr. Mann and the survival instinct that animates his betrayal of our main characters is perfectly legitimate. Cooper calls him a coward because he seeks to preserve himself at the cost of the mission, but we might be reminded that, at this point in the film, Cooper is guilty of the same thing. The elder Dr. Brand’s plan A is a hoax, earth is doomed, so why not return to your loved ones? Dr. Mann is completely justified in his actions, so why all the sinister music while he is doing his thing?
Love is transcendent, the younger Dr. Brand says, but what that means differs from what it means in a world created and sustained by a personal God.