This is another currency crank fallacy: that all interest received by banks is pure profit. Actually it is only the bank's gross income, out of which must be paid the bank's running costs (buildings, computers, etc) as well as staff wages but also interest to those from who the banks have themselves borrowed money (according to
Robert Peston, the "interest margin" between what banks charge for loans and what they pay out in interest is currently not much above 2%, ie if they charge borrowers 6% they pay lenders to them 4%). What's left is profit, out of which is paid dividends to shareholders, big bonuses to top executives or which is accumulated as more capital. Apart from the last, all the interest is distributed to people or institutions who will spend it and even the part transferred to the reserves as more bank will be spent in the sense of being invested in bonds. It won't be hoarded ("stockpiled"), as you seem to be suggesting. This is not banks behaving "altruistically" but the way they work.