What is the word for a deep desire that was prohibited?

forbidden fruit - The term comes from the biblical story of Adam and Eve eating from the Tree of Knowledge - the one thing that God prohibited Adam and Eve to do.

For example:

Mary made a point of telling her son not to play with the kids accross the road, but of course this was a forbidden fruit to Tom, and it made him want to play with them all the more.

The problem with drug prohibition is that it can be something of a forbidden fruit to teenagers looking to establish their identity, and doing what's prohibited and frowned upon can become an expression of that identity.

Movie censorship is a classic forbidden fruit problem - the act of censoring it makes people want to see it all the more.

OP requests a single-word that describes 1) a singular, strong desire 2) which is by circumstances, prohibited (but, nevertheless, pursued) 3) to negative effect (makes you do stupid things).

That’s an awful lot to ask of one solitary word, as a result of which (as I write this), of the 7 answers submitted, the only two that have positive votes are multiple-word answers, while the other five answers, all of which have suggested single-words, have received no votes at all.

A Google summary of the film Foxcatcher, relates:

When wealthy John du Pont invites Olympic wrestler Mark Schultz to move to his estate and help form a wrestling team for the 1988 Olympics, Mark sees a way to step out of the shadow of his charismatic brother, Dave. However, du Pont begins to lead Mark down a dark road, causing the athlete's self-esteem to slip. Meanwhile, du Pont becomes fixated on bringing Dave into the fold, eventually propelling all three toward an unforeseen tragedy.

One way of describing John du Pont's driving and prohibited motivation is a the French loan term "idee fixe," Anglicized as "fixation." Another would be "obsession."

Idée fixe

The words idée fixe also occur explicitly: for example, in Arthur Conan Doyle's Sherlock Holmes:

There is the condition which the modern French psychologists have called the “idée fixe,” which may be trifling in character, and accompanied by complete sanity in every other way. A man might form such an idée fixe... and under its influence be capable of any fantastic outrage.-—Arthur Conan Doyle, The return of Sherlock Holmes

An idée fixe is a preoccupation of mind believed to be firmly resistant to any attempt to modify it, a fixation. The name originates from the French idée, "idea" and fixe, "fixed." Although not used technically to denote a particular disorder in psychology, idée fixe is used often in the description of disorders, and is employed widely in literature and everyday English. (Wikipedia)

What is it, what nameless, inscrutable, unearthly thing is it; what cozening, hidden lord and master, and cruel, remorseless emperor commands me; that against all natural lovings and longings, I so keep pushing, and crowding, and jamming myself on all the time; recklessly making me ready to do what in my own proper, natural heart, I durst not so much as dare?.-—Herman Melville, Moby Dick

OBSESSION

1: a persistent disturbing preoccupation with an often unreasonable idea or feeling; broadly: compelling motivation ; (M-W online)