What, Icahn can fling random accusations but Andreessen can't? It's all just mud-slinging.
As for Andreessen's motive, I suppose he probably thinks Icahn is making a power play and is more interested in fending off Icahn than in defending himself in this particular instance. Icahn clearly wants Andreessen on the defensive, so it kind of makes sense, though it all feels a bit embarrassing.
I understand this is all mud-slinging and I think most of us agree that Icahn probably got more mud in his past (though I am sure someone will disagree).
The question for Andreessen is that did he think (and could prove) that he's a more ethical businessman than Icahn (note I am not saying a better person here) Apparently not, at least in the Skype sale.
As for Andreessen's motive, I suppose he probably thinks Icahn is making a power play and is more interested in fending off Icahn than in defending himself in this particular instance. Icahn clearly wants Andreessen on the defensive, so it kind of makes sense, though it all feels a bit embarrassing.