ComeWhine - it does not make any generalisations. It reports the observations of the survey and number crunches them to look at overall statistically significant outcomes. This does not 'generalise' in the sense of saying 'all bf babies are like this' and 'all ff babies are like that'. The behaviour is not defined as 'bad', though for all I know some newspapers may report it that way.
The purpose of these studies is not to make anyone feel guilty. Individual mothers can ignore, if they want to, safe in the knowledge that the majority of kids in the survey did not have the behaviour issues described anyway.
The useful purpose is to inform state expenditure priorities, training of HCPs, social care programmes, employment law and so on. Is it worth trying to support mothers to breastfeed and to breastfeed for longer? Does it make a difference and should we spend money on removing barriers to breastfeeding? Yes - there is sufficient evidence that this would be money well-spent.