Avengers 4 Theory: Does Tony Stark Have A Death Wish?
1. Why It's A Good Thing
It might not seem like a particularly positive thing for Stark himself to be so self-destructive, but it definitely serves a purpose for the Avengers. It makes him a weapon of significant size and impact, because it is combined with a singular focus on saving the universe (whatever the cost).
Each of the surviving Avengers has some element of bloody-mindedness about them: Captain America won't turn his back on a fight (particularly against bullies), Banner and Hulk are stubborn, Black Widow is staunchly focused and principled (so too is Clint Barton), Thor has been willing to give up his life more than once for greater causes... It's no surprise that they, along with Stark, are the ones left to fight Thanos.
And there's nothing more dangerous - as Thanos proved - than someone with principles fighting for what they think is right and willing to pay the ultimate cost. That's why the Mad Titan should fear Tony Stark.
As Thanos says in Infinity War, he's the right man to balance the universe because he's the only one willing to do it. To go to those extremes. The same can be said of Tony Stark, who is very much a mirror image of Thanos. He knows that going to extremes is necessary and he doesn't view the cost of his life as too much to pay if it means a victory in the long term.
Ultimately, Tony's commitment will be one of the most valuable assets in the war to come against Thanos and the fact that he now has unfinished business with the mega-villain should worry him.