Marc has already pointed out that he removed himself from the decision making process regarding the divestiture of Skype and fully disclosed his conflict. ebay held 30% to his 3% during all of this so Icahn's claims seem pretty baseless and should be easily confirmed or denied by another member of the ebay board with knowledge of the proceedings.
Andreessen doesn't care about the moral dimension, he cares about the practical dimension. This series of blog posts is aimed at EBay shareholders - he's trying to convince small-time individual shareholders that if they ally themselves with Icahn they're going to get screwed. (I assume he's running a similar campaign in person with the big-time institutional shareholders.) Smart money probably knows they're going to get screwed by allying themselves with Icahn, but there is an awful lot of dumb money on Wall Street, and they are easily swayed by just a little information.
I'm not sure that's a good defense: "He's killed twice as many people as I have, and he's been at it longer, too!"
When people so alike bicker like this in movies, they're usually about a minute away from kissing.