A student cited this link to an essay by Doug Egerton and Judith Mulcahey. The key passage:
"Despite the widespread opposition to the ACS in northern cities, the group was never the planter-controlled organization that Walker and its abolitionist critics claimed it to be, and assertions by modern scholars that proslavery activists endorsed the society in the hope of removing dangerous free blacks like Vesey are largely without foundation. Admittedly, in the border South, proslavery politicians such as President John Tyler and Secretary of State Abel P. Upshur hoped to use the organization to rid their state of free blacks, whom they believed inspired perilous dreams of liberty in those yet enslaved. But despite the racist tone of their public rhetoric, many white colonizationists privately harbored progressive views regarding black capabilities. Society spokespersons insisted that southern poverty was not the result of alleged African American incompetence, but rather that an economic institution based on unwaged labor deprived blacks of both the incentives and the education that made northern free wage workers so productive. Because many border state colonizationists boldly advocated the complete elimination of the African American labor force, slave and free alike, in the name of greater regional prosperity, Lower South planter politicians like Robert Turnbull of South Carolina bitterly castigated the organization as an “abolition society.”
"Modern historians also tend to regard any scheme of mass removal as an impossible one. But the society estimated the cost of sending one black settler to Liberia to be only twenty-five dollars. Since the black population during the early antebellum period grew by roughly six thousand people per year, it would cost Congress only $120,000 annually to remove every newborn or recently emancipated slave. Over the course of two to three decades, the white population would continue to grow, while the proportion of blacks in the national population would plummet, marginalizing unfree labor in the process. ACS defenders observed that a government that could force Native Americans to move west into Oklahoma was perfectly capable of compelling free blacks to sail east toward West Africa. Some politicians even noted that Washington could have conveyed 1.2 million black Americans to Liberia for the same sum that it spent crushing native resistance in the Second Seminole War."
What changes if we have to take the ACS more seriously?
Source: Encyclopedia of African American History, 1619-1895: From the Colonial Period to the Age of Frederick Douglass