Hi Kay,
Thanks for bringing this up again. Re-reading it, I’m really puzzled by Ven Thanissaro’s statement (mentioned in Bhante Sujato’s post you linked) that:
It’s sometimes understood as saying that we should be willing to sacrifice our lives to protect all others, in the same way that a mother would sacrifice her life for the sake of her child.
To me, the obvious way of reading the verse:
Even as a mother would protect with her life
her child, her only child,
so too for all creatures
unfold a boundless heart.
[Sujato]
As a mother would risk her life
to protect her child, her only child,
even so should one cultivate the heart limitlessly
with regard to all beings.
[Thanissaro]
Is that the boundless heart should be like the love a mother feels for her child, i.e.
“Have a boundless heart for all, like the mothers love for her child”, not
“Protect all others, like the mother protects her child.”