"Attacking the credibility of a source is an ad homenem (sic)argument. It's not a legitimate argument."

What arrant nonsense! Of course attacking the credibility of a source is a legitimate means of argument. Suppose a source was giving erroneous information on a regular basis, it is perfectly alright to point that out in rebuttal that their credibility is lacking.

Should we not always consider the point of view of person or group providing information? Whether information comes from The Wall Street Journal, The New York times, the White House Press Secretary, the DNC one needs to be aware of their biases and their point of view. So, too, with Palestinian spokes people or Israelis. Also, are they speaking for an organization, or expressing a private opinion (opinions, as someone pointed out are not facts? Are they speaking from first hand knowledge, or from hearsay? Do the deeds of the source match its pronouncements? All of those are fair argumentation.

The most egregious form of ad hominem attack I have seen at Mudcat was the discussion concerning Ann Coulter's comments on the Donny Deutsch show. I venture to guess that ninety percent of the anti-Coulter arguments were in effect "she's ugly, "she's a skinny bitch' and similar; precious few posts actually addressed the comments she made, or tried to rebut them. Those, my dear, were truly ad hominem arguments.