Pointing out errors is one thing, but you went on to suggest that rather than 13 billion benefit, longer breastfeeding might actually cost the taxpayer money, based on nothing but an unevidenced musing, and suggested that you wouldn't actually want the figures to be done because of a worry that it would destroy campaigns for longer maternity leave. If I read your paragraph correctly.
That is going a lot further than saying 'I think 13 billion is excessive because they didn't take into account blah'. It's trying to argue that supporting extended breastfeeding would be bad. That's not a neutral position, so I'm interested why. You are not simply pointing out errors with that speculation.