In Macbeth, what is the point of Lady Macbeth's baby imagery in Act I Scene vii?

This is a much-debated question by critics! Lots
of profitable time has been lost in my opinion by arguing about whether Lady Macbeth
actually had any children, how many, and what happened to them. However, such questions
seem to miss the point of what Lady Macbeth is doing here. Note that in this scene, her
purpose is to persuade Macbeth and convince him, in spite of his doubts, to kill Duncan
and commit the crime of regicide so he can seize the crown and become King of
Scotland.

In this context then, Lady Macbeth uses the
imagery about her baby to try and shame Macbeth into killing
Duncan:

I
have given suck, and know

How tender 'tis to love the babe
that milks me:

I would, while it was smiling in my
face,

Have pluck'd my nipple from his boneless
gums,

And dash'd the brains out, had I so
sworn

As you have done to
this.

Let us note what Lady
Macbeth is trying to do here. Macbeth has made the promise to kill Duncan and now he is
backing off out of fear or lack of courage. Lady Macbeth is saying that had she so sworn
to commit such a crime, she would have done that which was most horrible and alien to
her feelings, rather than break the oath. To emphasise the point she uses an act that
would have been most horrible and shocking to her feelings - the murder of her child
whilst it was at her breast - to underline the solemnity of the promise that Macbeth
made.