"The [OCCASIONALLY] drunk mother is not a problem because of the small amounts of alcohol in her milk, but because she may drop the baby.
(I have taken the liberty to insert a word into your phrase.)

  This is why, when patients ask me about drinking and breastfeeding,  I tell them that perhaps they should look at in the same terms as they look at drinking and driving.  If they are "too drunk" to drive, by legal standards, if not by their own, they may be too drunk to be properly responsive to their babies' needs, and should make sure that someone is available to take care of baby.  If they have so much alcohol on board that it is causing them to function poorly, it is probably still too soon to breastfeed as well.

This might be seen as too moralistic/prohibitionist, whatever.  I just call it being prudent.  I have never been able to drink much at a time, but always have enjoyed some wine, occasionally, with dinner.  (When I had my baby, I could drink about 1/2 a glass of wine before I got "silly.")  If someone told me I couldn't have that, I would have been upset and probably angry at the busybodies.  On the other hand, I have to ask, if a parent gets THAT upset that I might be trying to take away her alcohol, maybe she is drinking too much.

How much alcohol in a mom, at a given moment, or over time, can a baby actually handle?  Where does "occasional" and "social" drinking cross over to "problem" drinking?  And what point is "a little" alcohol during a day really "too much."  If a mother tells me she simply can't give up her glass of wine with dinner each night, does she have a problem?  What about if she can't give up her before-dinner-drink, plus a glass or two of wine with dinner, plus the brandy in her coffee afterwards?   

We tell moms that drinking in moderation is probably not going to cause 
problems, and we tell them how to lessen the potentials for risk to their 
baby, if they drink more.  That is all we can do, and then hope that their 
definition of moderation approximates our own.

I am reminded of a patient who delivered at our hospital.  In response to the
 initial intake questionnaire in the clinic, and again when she entered the 
hospital, she said she drank one or two glasses of wine each day, 
maybe three, usually with her meals.  She had a quick labor and easy 
delivery.  Sometime early in her postpartum stay, she started getting very 
shaky, literally and figuratively.  She was acting like someone who 
"needed" a drink.  Very tactful and gentle questioning, by an excellent 
nurse (not me), elicited  the information that her one or three glasses/day 
were actually two - three BOTTLES of wine each day.  (Well, I guess a 
bottle is a very large glass...) 

Sincerely,  Chanita, San Francisco