the intention of the idea is good but there could be some problems with the mechanism i think. what idf someone maliciously flagged another address for whatever reason? how can the owner of the flagged address remove the stigmata? how will such matters be resolved?
Suppose a malicious address is marking 1000 addresses as scam sending 1 finney for each address. In turn each of the wrongly-marked addresses are flagging the malicious address as scam are sending 1 finney each to mark the single malicious address, the number of SCAM_STAMP tokens associated with the malicious address will be at least 1000 times greater than any of the maliciously-marked addresses.
the balance of SCAM_STAMP tokens of each address is merely an index of untrustworthiness given by the community.
In order for the SCAM_STAMP tokens to be removed from one's balance, a 10 finney per token fee must be paid to ForgiveMe function, all finneys will be sent to whoever marked the address as scam. So if you want your address to be trusted, you would have to pay the fee to the community.
In the example above, the attacker would have to pay, after the attack, at least 10 ether for the trouble that it made (as the community reacted and fine it with an amount of SCAM_STAMP tokens)