DOS attacks are unethical and illegal. Exercising your 1st Amendment right to comment on their BS by flagging it as spam isn't. Sign up for a Yahoo account, subscribe to moveon.org's mailing list, then hit the "This is spam" button... Yahoo's systems, once they get enough people registering it as spam, will automatically filter it into bulk (spam) email folders rather than inboxes.
Ah the wonders of technology!
...not a bad idea.