I don't think its racist as such but there is a particular sensitivity about it.
There are genetic differences between different groups that affect lots of aspects of our health.
The issue is where value is attached to that difference. As in one group is 'better' than another rather than one group 'is more susceptible to this particular problem because of this evidence basis reason'.
The difference is subtle and controversial and should be handled with care.
Personally I think that speculating based on midwives tales alone and anecdotes off MN, is possibly not handling with care and is potentially dangerous.
Its quite a leap to go from asking what makes British women particularly unique genetically compared to other seemingly similar groups to singling out a particular thing in this way.
What you need to find to start talking about this as a possible idea is a correlation of rate feeding rates to the population of red hair / fair skin gene carriers. If this is the case you would expect a significantly lower breastfeeding rate in places where there is a higher proportion of red hair gene carriers.
There has been good research into mapping red hair genetics.
So is there a correlation?
map of red hair
It is hard to calculate the exact percentage of the population having red hair as it depends on how wide a definition one adopts. For example, should men with just partial red beards, but no red hair on the top of their heads be included or not ? Should strawberry blond be counted as red, blond, or both ? Regardless of the definition, the frequency of red hair is highest in Ireland (10 to 30%) and Scotland (10 to 25%), followed by Wales (10 to 15%), Cornwall and western England, Brittany, the Franco-Belgian border, then western Switzerland, Jutland and southwest Norway. The southern and eastern boundaries, beyond which red hair only occurs in less than 1% of the population, are northern Spain, central Italy, Austria, western Bohemia, western Poland, Baltic countries and Finland.
Overall, the distribution of red hair matches remarkably well the ancient Celtic and Germanic worlds. It is undeniable too that the highest frequencies are always observed in Celtic areas, especially in those that remained Celtic-speaking to this day or until recently. The question that inevitably comes to many people's minds is: did red hair originate with the Celtic or the Germanic people ?
Southwest Norway may well be the clue to the origin of red hair. It has been discovered recently, thanks to genetic genealogy, that the higher incidence of both dark hair and red hair (as opposed to blond) in southwest Norway coincided with a higher percentage of the paternal lineage known as haplogroup R1b-L21, including its subclade R1b-M222, typical of northwestern Ireland and Scotland (the so-called lineage of Niall of the Nine Hostages). It is now almost certain that native Irish and Scottish Celts were taken (probably as slaves) to southwest Norway by the Vikings, and that they increased the frequency of red hair there.
Based on that evidence, there is not a correlation that I can see...