So what it is “only her child”? You want to allow mothers to cause brain damage or kill “only her child”?
Oh. The risk is very small you say? It is also very small by MBP. Or driving. (Actually the risk of killing someone or getting killed driving is greater than doing MBP or nursing.)
So we all take small calculated risks every day, don’t we. If we can take these risks for nursing and driving, we can take it for following our religion. Religious practice (i.e. doing G-d’s will) is at least as well worth the very small risk as driving or nursing.
Surely those against MBP would similarly (to say the least) be opposed to the Akeidas Yitzchok. How dare a father plan on killing his child! Tendler would’ve likely called the cops to arrest Avraham Avinu and charge him with attempted murder.