Final answer:
The speaker's argument is effective because she appeals to the guiding principles of the United States and argues for a change in the way women are treated.
Step-by-step explanation:
The speaker's argument in the excerpt is effective because she appeals to the guiding principles of the United States.
By emphasizing that the formation of the Union was meant to secure the blessings of liberty for all people, including women, she highlights the contradiction of denying women the right to vote.
She argues for a change in the way women are treated by pointing out that it is a mockery to talk about women enjoying the blessings of liberty while they are denied the means of securing them through the ballot.