NEVARRRRRRRRRRRRRRR!!!!
Marth is the most manly character in the game and it's about time people realized it. Seriously, people like Captain Falcon and Snake are hailed for being so manly when they're honestly just compensating for their LACK of manliness. A true man doesn't need to walk around in a skin tight suit shouting "SHOW ME YOUR MOVES!" or "FALCON PAUWWNCH." Marth is so incredibly manly that he needs to appear so feminine to limit his incredible manliness--yes, Marth wears that tiara to prevent from manliness overload; last time he took it off, there were no survivors.
In fact, what really happens in his final smash is that after he thrusts his sword up in the air, his tiara raises a fraction of a milimeter, unleashing some of his overpowering manliness, thus the only possible outcome is the person or persons who are hit by his next attack immediately die, no questions asked. In fact, sometimes Marth kills himself with this attack because the Wii has a momentary lapse of understanding in which its mind is blown with Marth's manliness, but Nintendo quickly fixes the problem without you even noticing during one split second, because as we all know: Nintendo is magic. Even from the Fire Emblem game, they HAD to make sure that Marth somehow had an excuse to wear a tiara, because otherwise the game would be no fun when Marth killed EVERYTHING--even so, he still killed everything. The same holds true for Melee and Brawl.
When making his character, Nintendo reasoned that the tiara was still absolutely necessary to keep on his head, for fear that there would not be enough diversity in players, seeing as everyone would main Marth, or that their worst fears would come true: Marth, in all his manliness would come out of the game and slay the world, causing Jesus to ascend from the Heavens to rescue us all. Clearly Nintendo wasn't about to let the apocolypse occur, so they kept the tiara on out of fear of Marth.
tl;dr version: Marth is constantly playing with his hair to make sure the tiara is still on, so as to avoid all of our consoles exploding.
Edit: When Marth takes off his tiara, Chuck Norris dies.
