Ok, here's what I've heard about the money changers incident.
It isn't because the money changers were making money, it was accepted practice for them to sell unblemished animals to worshippers, to be used for sacrifice.
When Jews came to Jerusalem to pay their Temple tax, they could only pay it with the half-shekel. This was a half-ounce of silver, about the size of a quarter and the only coin which was pure silver, of assured weight, and without the image of a pagan emperor. Therefore to the Jews it was the only coin acceptable to God.
These coins were not plentiful and the money changers had cornered the market on them...so they raised the price of them to whatever the market could bear. They used their monopoly they had on these coins to make exorbitant profits, forcing the Jews to pay whatever these money changers demanded.
Jesus threw the money changers out as their monopoly on these coins totally violated the sanctity of God's house. These money changers called for his death days later.
I pulled that from this site, but I looked until I found something that concurred with my understanding.
The History of the “Money Changers”
I've actually heard more about this episode, but can't quite remember what it was.
