A theory they should think of is that condoms have toxic chemicals in them that make women depressed.

"Meanwhile, risky sex is usually associated with negative self-esteem and depressed mood. Among college women, risky sex includes intercourse without condoms, so we would expect sex sans condoms to be associated with more depressive symptoms, and more serious depression including suicide attempts. However, in the Gallup-Burch-Platek study, among women who "always" or "usually" used condoms, about 20 percent reported suicidal thoughts, but among those who used condoms only "sometimes," the figure was much lower, 7 percent, and among women who "never" used condoms, only 5 percent reported suicidal thoughts. (This study controlled for relationship duration, amount of sex, use of the Pill, and days since last sexual encounter.) So it appears quite possible that the antidepressants in semen might have a real mood-elevating effect."

They might want to see how women who have no sex ever feel but those don't exist.