[Prokopton]

It's hard to argue with you that they are scum. However, that type of response only brings back the typical "no you're the scum". I've always found it more effective to marginalize these people, and the best way I know how to do this is laugh at them. Not a deriding snicker, but a genuine "you are so silly" laugh. People hate to be laughed at. They will not laugh back but instead they feel a need to show that they are not "laughable". This usually brings on even more laughter.
Scum is OK with me, but I am laughing at their infantile silliness.

[Congressman Billybob]

Actually, the immortal Mark Twain fully agreed with your point. He wrote, "The only effective way to deal with a public humbug is with humor...."

John / Billybob