Origin of milquetoast and the negative meaning of milk in modern usage

Question

I searched the word milquetoast and found out that it is a very pejorative term used in American English (after a cartoon character- Casper Milquetoast) to refer to someone of an unusually meek, bland, soft or submissive nature, who is easily overlooked, written off, and who may also appear overly sensitive, timid, indecisive or cowardly (Wikipedia); the equivalent of a pipsqueak.

I’m quite taken aback and find it difficult to understand the connection between the word milk - originally associated with kindness and humanness, namely in Shakespeare’s work (milk of human kindness & milky gentleness )- and the negative attributes mentioned above.

My questions are:

How did this shift in meaning occur, and what’s the connection between milk and the negative meaning it acquired? Are there other words or expressions referring to the pejorative use of the word milk in English (American or other varieties of English)?

Milk of human kindness

Definition:

A phrase from Macbeth, by William Shakespeare, meaning humane feeling, concern for other people: “Everyone agreed that Houston was a brilliant thinker and an excellent lawyer, but some people worried that he lacked the milk of human kindness.”

Dictionary.com

Answer 1

milksop is a very similar word, which Merriam-Webster defines as

a weak boy or man

or

an unmanly man

The etymology given is

Middle English, literally, bread soaked in milk. First Known Use: 14th century

A Google search for milksop provides the synonyms:

namby-pamby, coward, weakling, Milquetoast

I have found no firm agreement on whether the term milksop for a weak person derives from that person's similarity to the dish of milksop (bland, insipid, weak), or that the person resembles the sort of individual who would be fed milksop (an infant, or sickly person). It is certainly one or the other.

There is a long discussion on the etymology of milksop in Current Methods in Historical Semantics(pages 26-29), which again reaches no firm conclusion on this matter, as far as my understanding of the passage goes.

However, it is certain that there is no development of milk itself as being a negative term.

Incidentally, sop itself appears to come from soup as indicated in The Register of the Privy Council of Scotland, Volume 6 (1599-1604), referring to a breakfast in 1602.

Unless milk is implied in the “ sowpe” in which the “quhyte breid" [white bread] or the “ait laif” [oat loaf] was to be presented, there is no mention whatever of that article. Porridge also, which we should have expected at the bursars' table, seems to be completely absent; for it is difficult to construe "ain ait laif in a sowpe" [one oat loaf in a soup] as meaning ordinary porridge even without milk. What we see is some kind of sop of oat bread for the bursars, and a similar sop of wheat bread for the masters, with cold meat and ale in addition. On this they began the day in Glasgow in the year 1602, - the breakfast of the Glasgow Professors not differing much, it may be assumed from that on which Shakespeare and other well-remembered Englishmen of that time were in the habit of beginning the day in London.

This passage may suggest that the nature of the dish is what is referred to when milksop was first used as an insult, as bursars, masters and professors at Glasgow, in addition to Shakespeare and other London gentlemen would not take kindly to being considered sickly by dint of their choice of breakfast dish. But, I concede that this is not proof and I consider the matter to be open to debate.

Answer 2

It's not that the person being described is like bread soaked in milk, it's that they eat bread soaked in milk.

Milktoast was a common dish (recommended even by physicians of generations past) for those who were convalescing, or otherwise weak of constitution. Thus, a grown man who was weak, meek, sickly, etc., would be called a "milquetoast" or "milksop" - implying that he was too fragile to even tolerate a regular meal.