I'm surprised to see MikeHearn and etotheipi saying to send back to sending addresses.
I would be really upset if I used my bitcoins to donate to Mark and they ended up in MtGox or instawallet's slush fund.
There isn't a way to safely return bitcoins and I don't think Mark blasting off what people gave him to who knows where in order to maybe satisfy potential bureaucrats complaints is terrible. Worse than never accepting them at all by long shot.
How about this:
Bureaucrat says: Mark we see what you did, pretending to return all of those coins by sending them to the sending address recorded in the blockchain, now you need to prove to us that you don't own any accounts which are attached to those receiving addresses. For all we know you made deposits to 1000 instawallets and 5000 MtGox deposit addresses before announcing that you were accepting bitcoin donations. You fully knew that some people would be paying from those popular wallet services and chances are that some of the coins would be paid from accounts with addresses associated to your accounts. So you 'returned' the coins to some of your own addresses. It's clever Mark, but not clever enough. The possibility that you retained any of those coins invalidates your campaign for breach of XXXX regulation.
Mark: .......
I don't understand. Those sending addresses are not black holes. The coins are not lost. It just has to be sorted out with Gox customer support, etc. Having a transaction ID and a signed message from Mark should be enough.
Plus, this is a condition that shouldn't happen -- there should be a huge warning on the donation page about it. If donors don't pay attention to the warning, then their punishment is dealing with Mt Gox support to recover the funds.
Perhaps for donations that happened so far, before people realized this, they can be returned via user-supplied address. That would be justifiable as "growing pains" of figuring out this process -- especially because it's not a ton of money Mark has received so far. However, future donations should follow this policy, and there should be some explicit warnings about it on the donation page.
Oh, I think I misunderstood you. You mean after he puts up a warning it is ok, I agree. Same as satoshi dice etc.
I was thinking about the situation where they didn't do that and want to get rid of the coins.
I know they aren't black holes, it could be an address assigned to another user (or Mark! as in my hypothetical) or an intermediate/cold storage address of the wallet provider.
Slightly different point also, you cannot in general assume that paying to an address is equal to paying a person unless they explicitly agree it will count as payment because they may have lost the private key or not be looking there anymore or sold it to someone in a foolhardy firtsbits collecting scheme.
Given the situation Mark is in it is impossible to return the coins to the senders, he's not accomplishing the desired undonating. But since he's only trying to convince bureaucrats who won't understand anything that comes with a sentiment of "I'm sorry I did something strange regarding money and I tried my best to undo it" will probably work unless they hate him.