The slaves would:
provide free labor and therefore an economic advantage to slaveholding states.
This is correct. It was a concern that those who were not slave owners would not be able to compete with those who were.
let white men build businesses rather than work on the farm.
This was also a concern. Theoretically, by enslaving others and making them work, white men would have a lot of time to build businesses.
not compete fairly with white youth seeking employment.
This was also a problem. Poor whites rarely had long contracts.
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The only one who doesn't fit is:
soon overrun the states without any knowledge of how to run a government.
This wasn't a concern because it has nothing to do with how to run a government or being able to.