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human
[The Avengers] Why the hell did SHIELD send Captain America to bring in Loki in Germany?

"I'd sit this one out Cap...these guys come from legend; they're basically gods," says Black Widow after Thor nabs Loki from the back of the plane. Good advice. He would get absolutely creamed. So...why would SHIELD send him in the first place? Captain America vs. an Asgardian? Please. How exactly did they expect that to go down? I think it's implied that Fury was the one who sent in Iron Man as well, for backup, but yeah, that's hardly any better. The way I see it there's no way SHIELD would have known that Loki would bow down after tanking a few punches from Cap. They're damn lucky they didn't lose three Avengers in about five minutes down there in that German courtyard.
gpt
One must note what exactly Captain America's power is. First off, he is a physically perfect human. He has what are basically superhuman reflexes and maneuverability. Against anyone with anything close to human reflexes, he has an inherent advantage in close quarters combat. 

However, this is not the biggest reason. Captain America is simultaneously the strongest and weakest Avenger. He is physically strong, fast, and strategic, and has great leadership. But he's close quarters, and ultimately human. SHIELD didn't know quite how Loki took control of people. All they knew was that Hawkeye, one of Fury's most trusted men, was quickly brainwashed into helping him, complete with all his knowledge. Now, herein is the dilemma. They need someone competent to take Loki down, but is not a major risk, should Loki take control. Tony Stark is capable of hacking into the whole SHIELD network. Black Widow has all the security codes, and the ability to infiltrate basically anywhere. And the Hulk? How could they risk him?

Steve Rodgers is a relic, he doesn't even get Pulp Fiction references, let alone be capable of hacking security. Worst case scenario, Loki gets a new bodyguard, who can be dealt with by the Hulk or Thor, easily. However, IF anyone can resist brainwashing, it would be him. If anyone could disarm a man a midst a crowd of hostages, it would be him.

Fury went against his superiors orders to send in Iron Man. It was a risk, for to lose Tony's genius would doom humanity. Captain America's value is in his leadership and ability to take on large numbers of enemies with ease. His loss would be great, yes. But to lose Iron Man, Black Widow, or the Hulk would be greater. To the people at the top, it was an easy choice. Send in one above average soldier who Fury talks up all the time to stop a situation. Little risk to perhaps end it there. Fury knew that they needed to guarantee Loki's capture as best he could, so he chose to send Iron Man, and risk losing Tony. The bet paid off.