The basic problem, to state it briefly, is to determine the factors that cause the individual to apply aberrant forms of stimulation to his standard genital equipment.

BWAH-HA-HA-HA!!
But really, how freakin’ difficult is it to figure out that a male who gets an automatic erection when he thinks about naked women will tend to seek real-life opportunities to “apply” a vagina to his standard genital equipment, while a male who gets an automatic erection when he thinks about naked men will seek to stimulate his standard genital equipment with the hands-on assistance of other males???
(Granted, why some penises respond differently from most other penises remains unknown to this day — but that’s not the question Rado asks in framing his discussion. Instead, he asks an utterly bizarre question about the psychological motivations of the penis’s OWNER. And I realize that sensibilities may have been more dainty in 1940 — thus the decorous phrasing “standard genital equipment” — but Rado was an academic writing to an audience of other academics, and should’ve been able to make the obvious point that male sexual behavior is “cued” to a significant degree by the “automated” responses of the male genitals.)
What’s especially mind-boggling is that Rado, being a male scientist, was presumably at some point a 14-year-old boy who had to deal with the acute embarrassment of spontaneous wood — unless, of course, he hatched fully grown from a space-pod…