They had to else else some of the cotton/agri growing states weren't going to ratify.
The founding fathers (ff's) were conscious of the down range implications and felt that letting future generations grapple with was the lesser of two evils. Leaving the south exposed to foreign influences was not an option to the ff's.
Agree. It was what it was, and only time could fix the issue of American slavery. And, it did. But, first, the country had to be unified and kept together.
No different than all over the world throughout history. This country did not invent the concept of slavery. Cultures everywhere used slaves, and some still do.
Chances are very good that an ancestor or two (or more) of yours was a slave....no matter what color you are or where you came from.