Article I, Section 8, Clause 4 of the Constitution does not ban the penalty of prison for debtors, but merely grants Congress the authority to standardize bankrupcy laws across states, since the proliferation of such laws among states hampered commerce. I don’t know where you get that this precludes debtor’s prison if the Congress so decides to allow for this through law.
The Constitution does not make it mandatory to go to school, but states most certainly do, and that is the power that is vested in states, as is the conservative position.
States following the Revolution began to impose restrictions on imprisonment for debt, as to duration, the amounts owed that would subject a debtor to imprisonment, etc. Eventually New York abolished debtors prisons altogether in 1831, and in 1833 the Federal government abolished imprisonment for debts being ordered by Federal courts. All the other states, following the lead of New York and the Federal government, abolished debtors prisons soon thereafter.