The Avengers missed a weapon, a Grenade that could have killed or defeated any person who harmed people or will harm them.
In Avengers 1, we saw that Dr. Erik Selvig used the Tesseract to create a portal in another Galaxy which lead the Chituari to Earth. In Avengers 2, we discover that all the things left in Avengers 1 was taken by Hydra. If Tony Stark and Erik Selvig used the Machine that made the Portal and use the Tesseract, they could make a Grenade which would open a Portal and make the enemy move to another location or make them go in another Galaxy and make them die. They could also make them go in prison or in the sky so they die when they hit the ground.