It might be more helpful for me if you just told me what happens if I play a Throne Room with a Treasure Map with 1/2 more in my hand.
I did tell you what happens. It's unambiguous from the general principles I mentioned that apply to all Dominion cards. You will find you have questions about seemingly complex card interactions over and over again until you learn to just
do what the card says (or as much as you can if you can't do some of it), even if it seems weird to you.
-When you say "you could argue that you can't do that part at all", well, what did I say? If you can only do part of something, do as much as you can. You
can do part of the thing (trashing a Treasure Map from the hand), so... you know, do that.
-When you say your group is confused because only "some [people] think that you haven't trashed two the second time", what madness leads the other people to think that 1 = 2? The second time, you have not trashed the played Treasure Map, end of story.
-If there is dispute in your group about the way a card works, and someone insists on an interpretation contrary to what the card actually says, it's probably best to consult the rulebook. And the case of Throne Room/Treasure Map with an third Treasure Map in hand is specifically explained in the Seaside rulebook.
I'm happy to patiently explain genuinely difficult rulings involving very subtle points - things like what happens if you play TR/Mining Village on a Possession turn, or what you are or aren't allowed to do when you play Quarry/Talisman/Royal Seal and buy a Mint, or what happens when you play Duration cards on KC chains - but this question and legions of others like it come down to just doing what the card says, or failing that reading the card FAQ in the rulebook.