How it fits together
Taxes pay for government services and national responsibilities. The Constitution gives Congress power to collect taxes, and specific tax laws determine what people owe. For the civics interview, “required by law” is an accepted reason to pay federal taxes.
A closer look
Selective Service registration is separate from joining the military. The civics question asks why registration is important, not whether a particular individual must register. Use the Selective Service System’s current guidance for personal obligations and any changes to the registration process.