I have no problem with breastfeeding in private or public however, I have a theory as to why people might find this kind of thing strange. I'll freely admit that is a theory that is entirely plucked out of my ass, so feel free to demolish it:
I think they chose well. Well in the sense of gaining maximum publicity. WHO currently recommend feeding a child until age 2 as far as I know. Some people go longer, some people go shorter. Arguments for both abound. If you wanted to create maximum debate and controversy therefore a child age around 3 is likely to do just that. It is right on the border line of all kinds of arguments on the subject.
So the cynic in my just thinks that picture was chosen very deliberately to sell copy.
I have long been interested in the breast feeding debate though. On a lot of forums I have followed people arguing about breast feeding in public and the like and heard how angry it makes people to see such a thing. I have my own theory, also plucked out of my ass, as to why so many people get so riled up over such a "natural" thing.
And that theory is that it is actually BECAUSE it is natural. Many humans want to think of humanity as being somehow above and beyond the animal kingdom. There is plants, there is animals and there is US and we are special. Anything which reminds people of our animal origins and affinities is sicking to such people and makes them angry. Breast feeding is one such thing. They want it hidden away because it is a reminder of just what we actually are.
I rather think my theory also goes some way, though clearly not all because of other religious reasons, to explaining some peoples hatred for Evolution. Evolution Theory places us very much as "just another animal".
We are special enough without having to pretend we are something we are not... or more precisely... pretending we are not something we are. But those horrified by the implications of breast feeding and evolution will forever stand up against public displays of either. Ironically I think such emotional immaturity rather takes away from what makes us special, the opposite of what they intend by exercising it.