Causing anyone undue harm, whether physical or mental, is where I draw the line. (I wouldn't really punch someone in the throat - I was exaggerating a little).

But attitudes that cause people shame and embarrassment are destructive. Do you not agree?

Most nursing mothers in our culture cover up. But it's often at great discomfort or inconvenience. Just so certain people will be spared the shock at catching a glimpse (if they happen to be staring in the right spot) of a nipple.

The embarrassment at seeing a bare nipple is self-imposed (completely internal to the person seeing it), while the embarrassment of a nursing mother at having to feed her baby while in public is societally-imposed. I don't see a rational basis for the embarrassment at seeing a nipple outweighing the embarrassment of a nursing mother which requires her to cover up. Causing shame for doing such a natural and important task is not consistent with a society that values not harming its members. Thus, it's wrong, if that's what your value is.