Answer:
By banning the importation of slaves after 1808 in the Constitution, the critics of slavery hoped to accomplish the following:
1. Gradually end slavery in the United States. The key argument was that if no new slaves could be imported, the existing slave population would die out over time since slaves could not reproduce fast enough to replace those who died. This was seen as a slower but more politically feasible way to end slavery.
2. Weaken the economic power of the slave states. Depriving the South of a continued supply of slaves from abroad would undermine the viability and profitability of the slave-based plantation economy. This could potentially lead Southern states to abandon slavery on their own.
3. Align the United States with the moral position of ending the slave trade. Banning importation of slaves would allow the U.S. to take the moral high ground internationally and be seen as working toward the eventual abolition of slavery.
4. Limit the geographic expansion of slavery. By restricting the 'import' of more slaves, critics hoped fewer slaves would also mean fewer slave states, placing political limits on slavery's reach.
So in summary, critics of slavery saw the 1808 timeline as a compromise that could eventually achieve their goal of a slavery-free America through economic, political and moral pressures, even if full immediate abolition was not feasible at the nation's founding.