Fuck Starlord, seriously. Dude fucked EVERYTHING and EVERYONE.
The theme of the movie seemed to be Sacrifice, and what people were willing to do to achieve their goals.
Star-Lord wasn't willing to sacrifice Gamora (until it was too late), Gamora wasn't willing to sacrifice Nebula, Scarlet Witch wasn't willing to sacrifice Vision (until it was too late), Cap wasn't willing to sacrifice ANYTHING. Even Loki wasn't willing to sacrifice Thor at the beginning. Any one of them could have made the sacrifice and stopped him from gaining or learning where the stones were.
Only Thanos was willing to make the sacrifice to get what he wanted by killing Gamora. Except for Dr. Strange, who sacrificed the Time Stone to save Stark. He made it very clear he didn't care about anything but protecting the stone. I assume that whatever future he saw where they were successful, Stark was alive. So he knew the only chance they had was to make sure Stark was alive, even if it meant sacrificing the stone. ---
