I suspect the “loose vagina” idea spread because it’s stupid and simplistic. Research shows that simple-minded nonsense spreads like wildfire precisely because it doesn’t require any brainpower on the part of the receiver, whereas complex ideas do require some cogitation and in general we’re evolved to avoid that whenever possible. It’s the same reason we have flat-Earthers, anti-vaxxers, and Trump supporters. All of this misinformation harms a great many people but I can’t see any way around it now that social media spreads untruths at literally 99% of the speed of light to an always-receptive audience.