Vinsin pointed out a situation where you took control of an account to increase your chances of repayment and the whole transaction was out in the open, transparent for to the whole community to see.  I have no objection to a lender operating as you have.

I do object to the use of the word "collateral" in such a situation.  Collateral implies value, and in order for the account to have monetary value it would need to be sold to compensate for a defaulted loan.  I think we all agree that selling accounts is a shady practice.  As long as the lender doesn't see the account as having any monetary value and only uses it as leverage to increase his chances of getting repaid, I don't see anything wrong with the practice.