During the debate over reconstruction plans, one leader voiced this opinion Southern institutions "must be broken up or relaid or all our blood and treasure have been spent in vain"Who most likely expressed this opinion?

Thaddeus Stevens

Explanation:

Thaddeus Stevens who lived between1792 - 1868, was a member of the United States House of Representatives from Pennsylvania in 1860s, he was considered to be one of the leaders of the Radical Republican faction of the Republican Party.

He is well known for his fierce opposition to slavery and discrimination against African-Americans. In his attempt to end slavery, he suggested during the debate over reconstruction plan, that Reconstruction should "revolutionize Southern institutions, habits and manners, and must be broken up and relaid, or all our blood and treasure have been spent in vain."

Hence, the correct answer is Thaddeus Stevens.