Princess Peach is unsurprisingly the insidious love spider at the centre of this whole web of deceit. She may maintain a regal facade, in in truth she's nothing more than a self-serving harlot with the morals of an alley cat on heat and no higher priority in life than the massaging of her own needy ego.
Let's look at the evidence shall we? She's been 'kidnapped' by Bowser a grand total of nine times so far, and that's just counting the core Mario games. Is castle security really that lame? You'd think after the first incident that the Mushroom Kingdom wouldn't be taking any chances with its monarch, but if Peach's story is to be believed (which is isn't) then the royal home is less secure than a sleep-deprived Woody Allen on a bad acid trip. No, we strongly suspect she's in on the whole sordid deal.
Getting herself intentionally kidnapped by Bowser? Whyever would she do such a thing, you might ask. Well put simply, Peach is a big old attention-whore, and the mis-guided sense of worth she gets from Bowser's actions coupled with Mario's endless willingness to come running whenever she calls gives the miserable, shallow-hearted bitch exactly the two-hit combo she needs to make herself feel good.
Why does she need the constant superficial reasurrance? Well until the Mario brothers turned up, she was the only human character in the whole kingdom. With no-one but bubble-headed fungus to relate to she must have got pretty lonely, and she now wildly latches on to any attention she gets, positive or negative, as a result. And now we come to think of it, how the hell can she be the Mushroom Princess if there's no Mushroom King or Queen above her in the royal hierachy? They may have died, got sick of her crap and left, or even sent her away to the land of 'shrooms as punishment for being a prissy wanker, but whatever the reason for their absence, a lack of parentage has probably only fuelled her needy attention-seeking.
Though none of that justifies her behaviour, naturally. Her coping mechanisms have all the depth of a puddle on a hot day, and she's screwing people over left, right and centre as a result. Of course, the first kidnapping was probably genuine. Apparently in SMB1 Bowser went after her because she had the power to stop his magic. But everything since then has been for her own ends. Is it a coincidence that she actually got her shit together and helped out in the American version of SMB2, only to go into a submissive capture-frenzy once Mario went over to Sarasaland to rescue Daisy in Super Mario Land? We think not. She was jealous and she wanted his attention all for herself.