Answered

How is the use of "liberate" a good word choice to help develop the author's purpose of improving leave for all parents?

a. The connotation of the word is weaker and does not encourage action.
b. Liberate is associated with rebellion and great change; the use of this word encourages others to act.
c. Liberate has to do with releasing guilty prisoners; so the connotation of the word helps us understand that work is just a metaphorical prison.