samstown, all those are valid questions, but good research allows for them. It's always been known that all SIDS cannot be explained by one single factor, once you discount the 'mystery virus' theory (which has not been taken seriously for decades now). SIDS appears to be a mix of environmental factors (smoking, feeding method, place of sleep etc ) and social factors (deprivation) as well as physiological factors (pre-term birth; illness)....but you can see that all of those 'overlap' in some way (so for example poorer mothers are more likely to smoke, and to give birth pre-term, and to not breastfeed).
But good research, with enough 'cases', can isolate these different factors, and assess their individual impact.
When it comes to sharing information with mothers and fathers, language is important, to avoid preaching or judging. This is why we have ended up with parents believing that 'breastfeeding is better than formula feeding but formula feeding is not harmful.' The fact is that breastfeeding is the physiological norm - it's what babies 'expect' to happen and what their own bodies are prepared for. Anything that is not breastmilk falls short of that and there are health consequences.
In a developed country like the UK, you don't really see the consequences - the baby who has gastroenteritis is cured, the baby who gets an ear infection gets better. Most babies - breast or formula - get gastro or earache at some point anyway. It's only when you look at hundreds of babies and compare them, and see the incidence of gastro and earache is significantly higher (ie consistently more episodes per baby, when you crunch the numbers) in non-breastfed babies, that you see the effect in the UK (there are other effects - I have only picked on gastro and ears because the research is especially strong). That clearly shows that formula feeding is not just 'not quite as good as' breastfeeding in some sort of abstract way, but actively harmful.
Now, that has to be set against the risk to babies whose mothers struggle with bf and become miserable and even depressed - physical health effects of not breastfeeding are not the full story by any means.
It would be daft to insist that all mothers 'ought' to breastfeed whatever the cost to their families.
Hope that explains it a bit :)