As Cosmosis says, there is no such thing as quality of milk problems. Yes you can get tired and run down, but quality of milk not a problem that exists except in the minds of people of my mum's generation, who were fed a lot of myths about breastfeeding at a time when formula was being pushed very hard at mothers.
Round the clock breastfeeding for months is not going to cause problems with 'milk quality', and it takes a lot to interfere with quantity.
There is nothing 'militant' about that statement either. Here is a FAQ page from LaLecheLeague.org.
'Myth 10: If a baby isn't gaining well, it may be due to the low quality of the mother's milk.
Fact: Studies have shown that even malnourished women are able to produce milk of sufficient quality and quantity to support a growing infant. Most cases low weight gain are related to insufficient milk intake or an underlying health problem in the baby.
Mohrbacher, N., Stock, J. BREASTFEEDING ANSWER BOOK. Schaumburg, Illinois: LLLI, 1997; 116-32.
Wilde, C. et al. Breastfeeding: matching supply with demand in human lactation. Proc Nutr Soc1 1995; 54:401-06.
Myth 11: Poor milk supply is usually caused by stress, fatigue and/or inadequate fluids and food intake.
Fact: The most common causes of milk supply problems are infrequent feedings and/or poor latch-on and positioning; both are usually due to inadequate information provided to the breastfeeding mother. Suckling problems on the infant's part can also impact milk supply negatively. Stress, fatigue or malnutrition are rarely causes of milk supply failure because the body has highly developed survival mechanisms to protect the nursling during times of scarce food supply.
Dusdieker, B., Stumbo, J., Booth, B. et al. Prolonged maternal fluid supplementation in breastfeeding. Pediatrics 1090; 86:737-40.
Hill, P. Insufficient milk supply syndrome. NAACOG's Clin Issues 1992; 3(4):605-13.
Woolridge, M. Analysis, classification, etiology of diagnosed low milk output. Plenary session at International Lactation Consultant Association Conference, Scottsdale Arizona, 1995.
World Health Organization. Not enough milk. Division of Child Health and Development Update Feb 1995 21. www.who.ch/programmes/cdr/pub/newslet/update/updt-21.htm'