Charities hate this. Ringfencing costs them a ton of money to track, exposes them to legal liabilities, does little good, is often entirely meaningless given the fungibility of money, and reduces flexibility. The way I put it would be this: if you don't trust them to spend your money well, why do you trust them to spend a restricted donation? Shouldn't you find a charity you do trust? There's so many out there, after all.