I posted this as a response to another's question but it's also what I would have said anyway... :)

I believe Jesus was outraged because the selling of sacrifices at outrageous prices kept the poor from atonement. Blood sacrifice was necessary the moment Adam and Eve disobeyed for it took an animal skin to clothe them. You know the term, "scape goat" - I had a Sunday School teacher explain this to me. When the Hebrews were brought from Egypt and erected their temple, of which Aaron (Moses' brother) was the high priest, the people could not enter the Holiest of Holies. Instead they wrote their names on a ribbon, it was attached to a goat. The high priest would slit the throat and set the goat running. The goat's blood covered the sin. I cannot tell you why the "wages of sin is death" but I do believe that what those men in the temple were doing prevented people at that time from atonement. God's will is that none should perish and He becomes angry to see His children denied.