I will tell you why. Have you read the other answers? Read them. And then come back and read this one last. And then you will judge who has told you why. I recuse myself on that one - the call is yours.
Why do people think of the danger of beautiful girls?
Because they know. They know of the danger, what if I stood up and declared to myself, in my inaudible mind-voice, “The girl is MINE. She is beautiful and has been nice to me as a regular habit!”
It would have no effect. Nothing changed. But then what if I declare it audibly, to her in her presence?
And then what if the girl (well, woman really, but this one gendersexually identifies as “girl” and has made it known, this preference is hers, and so she is) were to rise and declare, “The girl is not his. He has confused my innate habitual sweetness with one and all as a claim on my favors! No dice.”
It would feel like a broken bone in the heart. Or a bad sprain at least - and a heart-sprain, which is imaginary, can take years to heal. Where a normal sprain heals at medical rates. Which do you prefer? Spare the heart, give up the ankle. You’ll thank me in relatively few weeks.
A girl like that, beautiful and sweet and true, is like a devouring monster from the inside of a pretty sweet dude who, though, is a little on the hapless side, and lacks self-control and a certain purity of purpose (I don’t mean “puritanical,” please - get your mind from the gutter and rinse it off! Do not wash it - brainwashing is not the solution. Use tears - they smart a bit, but it rinses you clean with catharsis).
Even a bold, hard man, such as myself except bold, and hard, is in danger of heartbreak and heartache from a woman whose beauty has won him, but who will not herself be one. Or won. Whose fault is that? It is not hers. We have no claim on her but the claim she gives outright - which she is free at all times to revoke. We are all free to choose what we give of ourselves, and to whom - and what we shall keep.
In short, the only man to whom a woman is not dangerous is the one who despises women, who sees in them only an instrument for personal gratification: ego (personal or social worth) or id (the genitals). Such men have other things to worry about, though, principally repulsiveness if their hearts were known to one and all. Or the ancient ache of alienation, self-loathing growing to hatred of all, should their hearts be known to none. That’s a no-win deal, people.
Homosexual men, too, are relatively out of danger, in these dangers of the womankind. As are heterosexual women. Trust me, though, they have their own challenges in this world. Bigots galore, misunderstandings and stereotypes - you name it. Most of all, men.
But enough of the danger of men.
That is the danger of woman to man, heterosexually. There are other dangers of course - she could knife you as easily as anyone, if you’re caught unawares! But I sense the heterosexual danger to men (and the homosexual danger to women too, I suppose, but I feel as if being women, lesbians have an insight which spares them much of this weird othering of others of their gendersexual preference) is the thrust of this question! It is real. As real as doves and serpents - these are not made-up mythological figures, though of course they pull double duty there. Your only course: be true. Lead always with your own real likes, wants, needs and loves. These will ward off those who are no fit match for you, with whom match would only be misfit and misery. And it will shine up the world around you like a beacon for those whose likes, wants, needs and loves are good for you, like yours.
Basically don’t make decisions about other people, where you don’t really know. Don’t prefer some made-up thing and want that. Prefer to honor who is in front of you, to find out who she is, and so discover in getting to know each other what you could be to each other. What she thinks about that is key.