You know, I conspired something similar to this long ago, when I explained (with logical reasoning) that Bowser and Peach are an item, and Mario is just dense.
it has been shown in several Mario games (notwithstanding Super Smash Bros) that Peach has no problem defending herself when it comes down to it. So why get "kidnapped"?
Not to mention that Bowser doesn't need to kidnap someone to get Mario's attention. He's the self appointed leader of Mushroom Kingdom, and if he desired the official role that badly, he could have just killed Peach off.
Mario (in some instances) assume that she's kidnapped and goes to rescue her, and normally Peach would be locked up if she was actually kidnapped, right?
But no, she just gets put in the next room, unchained, exit is right there in her face and everything.
Not to mention that Bowser had kids, hmmm. You think he can a-sexually reproduce? Or does a female of his kind exist? Or is he a she?
The second solution is only speculation never to have been proved, the third is just bullshit.
The first one seems logical enough, if he's a giant spiked shell turtle who can breath fire, what can't he do?
But that still doesn't answer the question of why he kidnapps the princess so much. is it even a kidnapping?
Well, fine point. It can be summed up with some "what if" kinda logic, but we all know why.