If you go out to eat do you not tithe (tip) the wait staff. Its not mandatory yet to tip the waitstaff (waiter & waitress, etc...) nor is it mandatory to tithe to God (the needy, your church, evagelists, etc...).
The money changers setting up their booths on church property for personal gain is like you going to a restaraunt and demanding service and then not tithing (tipping) the Wait staff. I suppose this is why were seeing an increase in the service fee in respect to the tithe (tip) to the wait staff in respect to how the world tithes.
If you go out to eat and do not tithe (tip) do you feel guilty about showing your face in that restaruant, etc...