It may help the greater good in the long run, but that is debatable. I used to forward my junk to spamcop and frankly that doesn't get you anywhere in practical terms of ridding yourself of spam. Even though they put my name it, I must assume they meant it for someone who cared. You are saying that your address is not a valid recipient for their junk. It is not unethical or dishonest to bounce a message. If I can write 'return to sender' on snail mail. If you didn't ask for the email you have every right to fight back in a technological sense. Or maybe you trust them.If so, I have a deed to the Brooklyn Bridge I want to sell you. One sure way of getting your address enshrined as valid is to use the 'unsubscribe' link that comes in most (and works in some) spams. I also suspect that bouncing unwanted mail to 'legitimate' spammers like '' or '' will save your address from being distributed later.when they sell their list. Even though the addresses they use appear to be dead.I also think they too have tricks to make you think that.
I also think some spammers do try to get rid of bad addresses in some automated fashion. I bounced 700 messages the first time and have been checking back about once per week. It was basically useless so I could experiment. It was a long-forgotten address that was listed on a site I designed.
I had an account that was getting hundreds of spams a week.