I actually liked the idea you quoted, and have two answers for you:
1) Is banking not the issue? Thus, financing religious crusades avoiding Banks?
I have no idea what this statement means.
2) If the Lord of the region your crusaders draw from is a believer, then you can still do it. He will simply collect the taxes and deposit them in the temple again, for the crusaders to draw on. It would even create some nice possibilities of conflict, with the Lord sending back all, part or none of the money deposited. Corrupt local lords profiting on devout foreigners? Crusaders having things more difficult by avoiding the normal legal banking system? All very good to me. What do you think about it?
It also does nothing at all to prevent the most egregious problem of guilds/religions as banks, which is the lord being the one doing the banking. The money taxed form the withdraw is then handed to the person doing the sheltering. And in the process you screw over the people taking gold out for perfectly legitimate reasons, by giving them much less of what they are due.
