An eye for an eye

Romeo was over come by fury, when Mercutio was killed. He lost one of the closest people to him and he couldn't take it. He changed into someone completely different than himself and avenged his fallen comrade. I do not know if I support what he did but I certainly respect it. Something had to be done but I don't know if had to be as severe as the first act. In this case both families were left to mourn, and no family won, so why was this act committed?  Why did this happen, no one gained anything, but only lost someone they cared about. When romeo finally finished him, we were in so much shock that time almost stopped. I snapped out of it and told romeo that he needed to run, the citizens are up, and Tybalt is dead. Don't just stand there, run if the prince catches you, you will get the death penalty.  (III,1, 94)