I feel like I'm repeating myself here (and perhaps this is a point that Googlers will never grasp, 42 shades of blue and all that) but many things can't meaningfully be expressed as a cost-benefit analysis. In this case, if you had asked me before the switch to come up with a cost benefit analysis (assuming I worked at Google and had the data) I could probably have come up with some figures, but the size of the errors would have been so huge as to make the exercise pointless.

Are you arguing that people sat in Google and seriously believed they were able to accurately quantify the cost of a huge raft of negative articles across the mainstream media and a bunch of the most popular users of the site shutting off their comments or leaving the site? (Assuming they even predicted the possibility of that happening). I just don't believe anybody can put a cost on that in advance. If that is really how decisions are made in Google then it is hardly surprising that their brand is so damaged.

Throwing around numbers is easy. It doesn't make the numbers right or relevant.