Are you hypothesizing that the net amount of transaction fees paid on the Ethereum network will be higher if you accept the donation, compared to if you don't accept the donation? I have a feeling that you might be accidentally comparing to a scenario where the donator does not donate and subsequently never transfers that cryptocurrency anywhere ever. This is not a realistic scenario. The donator is almost certainly going to transfer that crypto somewhere anyway, so it doesn't appear to me like your action of refusing the donation reduces the net amount of transaction fees.