Hermit crabs are decapod crustaceans of the superfamily Paguroidea.
Most of the approximately 1100 species possess an asymmetrical abdomen that is concealed in a scavenged gastropod shell carried around by the hermit crab.
Homosexuality /in general/ IS harmful though, evolutionarily speaking. If everyone was gay we could not continue as a species (obviously). To say flat out that it's harmless seems like a gross over simplification and jumps the gun.