I think categorically ignoring the volition of a person just because they are legally a minor is a bit naive. Obviously he was the older and should have been mature enough to know it was wrong, but it doesn't mean she is incapable of some degree of calculation. Though its debatable if she did or not here.
But many people's axiomatic beliefs seem to be that in these situations minors are completely absolved of their actions, which i think is a dismissive take due to philosophy/ethical zeitgeist.

That's not the implication that came across in the movie, IMO. It was more like she seduced him, which ended up ruining his life.
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Why would the victim be punished? Dave was the adult in the situation and he's the one who groomed Tracy and instigated the relationship. Jim wanting Tracy to suffer for Dave's actions is indicative if his poor character.

I think he was angry that his friend Dave got fired over the whole mess with Tracy while she didn't get punished at all. He wanted Tracy to suffer in some way. It is like later when he suspects Tracy of sabotaging the posters and Tammy confesses falsely. He thinks Tammy got away with something again.

He has a thing for her and he knows how weak he is when it comes to other women, so, yeah, at least on a subconscious level, this is the most self-aware action he takes in the movie. Of course, he is so self-important that he convinces himself (and tries to convince us) that it was all about "stopping Tracy".

Mr. M hated Tracy for being the way she was.
Yeah, the main reason he disliked her was definitely tied to the fact she was a complete and utter bitch. That said, it's pretty strongly implied she DOES have a thing for seducing/flirting with older guys to try and move ahead. She was definitely being flirty with him in the car scene with her comments about "working really closely together" and they imply she did the same to the senator at the end.
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Hmm he did picture her head while he was porking his wife

I think this totally sailed over your head because you are not a man.
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I think you're right, but I don't mind admitting it about myself.
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Yeah, you are probably right, they could have expanded upon it with another line or two, McAllister was clearly open to seduction as we seen with the neighbor later in the film and most 35 year old men getting board with their marriage would have a hard time resisting a 17 year old blond power player seducing them (although they would never admit it, even in anonymous chat rooms most of the time).