A lot led up to the end of slavery and I was only addressing your original point. The founders of the US did not IMPOSE slavery on the country. They recognized that it was immoral and sinful, however they also recognized that the Constitution would not be adopted by all of the colonies if they addressed it immediately. However, they did present a constitution for adoption that provided the tools to future generations to resolve slavery.
Slavery existed long before the founders and although they were uniquely suited to the founding of the United States, they could not solve all evils in one fell swoop.
Agreed in part, the founders could not solve all issues but tabling them till 1861 was not the best choice either.
That the DEMOCRAT party made the post civil war era attempts to set the slaves on the path to FULL economic parity is probably more to blame at this point than slavery itself.
Read the list of civil rights laws passed by the post war Republican congress as attempts to solve the issues (none stong enough or at least no enforced enough sadly)