Well, exactly. Therein is the crux. Is that worth the extra conversions (which may mean more active users, an important metric to consider)?
As I said I don't know.
But you know. In my experience bad Karma has a funny way of fizzling out. Remember Climategate? Mostly fizzled out. I bet plenty of people have forgotten all but the broadest details as they read the latest climate blog - give it a few months and people won't bring it up any more. The Parliamentary expenses scandal in the UK? All fizzled out after a couple of months despite being pretty much wide scale "fraud". It's no longer as interesting as the budget. Last years financial melt down - pretty much the biggest example of "bad karma" we could pick. Where are all the vocal "we must punish the bankers" people now? (I realise there are vocal people still - and good on them - but the general public isn't all that interested now, they are still choosing to use Barclays etc.) How much is the Oil spill on national news right now?
Point is: heat lasts for a short while. The play you have to make (and I make this as a general point, I have no idea of Posterous' aims) is whether once that heat dies everyone sorta forgets it. If in a month the only people still bringing it up are the Tumblr fans then they will have succeeded. Sure someone in a few months might think "actually I will use Wordpress, I remember Posterous were jerks" - the play is how many are left thinking that.
And, finally, "there is no such thing as bad press" (certainly not bad press like this)
Disclaimer: I don't approve of what they are saying.