I mean, porn and imagined girlfriends are a problem. A bit like alcohol, sweets, and in general addictive things.
They, eh, allow one to alleviate loneliness and sadness, but not really.
Now fantasy girlfriends are an existential threat to women? If a man wrote about how he has to compete with romance novels and sex toys he would be derided as a fragile loser.
They are a threat to women in that they supposedly make men a bit more likely to become fragile losers. In perception at least, I think in reality such men would become alcoholics or something else instead, or would just develop their imagination.