Breastfeeding shielding child from Depression?

I recently read this article/study, with the title: "Breastfeeding in infancy may shield adults from Depression". The title caught me and I found it very interesting. I am openly pro breastfeeding but also very sceptical about how breastfeeding is promoted or used.
As I've mentioned in another post, breastfeeding is a very hot topic in mothers' discussions, provoking extreme reactions. I have also said that breastfeeding is not only the natural act per se but can and usually is very symbolic about female sexuality, fecundity, power, ability to be. Mothers attach knowingly or unknowingly intense emotions to breastfeeding. Some feel like failures if they can't establish "it", others feel less womanly, others feel that breastfeeding is the main median to prove their worth, yet others relive through breastfeeding a union that they themselves missed as children. Of course there are always the mothers who breastfeed simply, just as nature intended, and mothers who for their reasons opt out of breastfeeding (and believe me there are many reasons and sometimes heartbreaking ones).
Now to get a study which basically says to mothers "breastfeed so you shield your child from depression" is a huge blow to all mothers... Why? Do mothers need more guilt? Do most mothers know how to read a study of this sort? Look at how many "subjects" were used in the study, the methodology, the interpretation of the results?
How can a study of this sort establish what the breastfeeding mother is thinking/feeling/doing when she is breastfeeding her child? How many mothers having themselves psychological difficulties breastfeed and at the same time feel numb (in that case what kind of "psychological milk" is the child getting)? And how many mothers don't breastfeed but give the bottle with warmth and care?
Yes, the research idea is interesting. No, the claim it makes in the title can't be established by this specific study. And to cut a long story short, it is not the breastfeeding that makes for a smooth, secure bond between a mother and her child. It is her concern, her warmth, her keeping the child in her mind and in her heart at all times. And that kind of mothering, with all its faults and imperfections is the kind that brings up adults "shielded" by depression.