kaansmum - interesting post. The 'milk of human kindness' which (I think) comes from Shakespeare) is a pun - the milk of human kind (ie the human race) is what it is, of course, and then Old Will (if it was he) stuck the 'ness' on the end for the wordplay. I agree about the desired impact of the slogan - it is to make the act of breastfeeding seem loving and kindly, and by implication, anything else seem 'less' loving and kindly.
This is the way advertising works, whenever there is an alternative product/service available. My local plumber tells me his service is 'fast and professional' and by implication, Fred Bloggs down the road is slow and sloppy.
The formula milk manufacturers use the same techniques. The slogans tell you than Brand X is 'closer by Nature'...closer than what? Frogs legs? Spaghetti hoops? No...'closer' than anything else you might use instead, and while the direct comparison is to breastmilk, by implication, with the use of word play, it is also saying you will be 'closer' to your baby, in the way Nature intended, if you use this product.
Do the mothers who use a different product feel attacked for not being close to their babies? I think not....because they know how advertising works.
Now - you are pleading a special case for mothers who use formula instead of breast, and I think you are right to do so, because breastfeeding, and breastmilk, is more than a consumer product or a consumer choice. Feeding babies is a sensitive issue for all the reasons you outline, and if we play on this aspect too much, then we risk upsetting women. Far better, in my view, to have a less emotive slogan that does not play quite so clangingly on the emotions.
One Scottish health board had a campaign with the slogan 'you can't get fitter than a breastfed nipper' which I think has it just right.