Where, pray tell, does it say that? Post it, please.
Read the Suspension Clause. Article One, Section 9, clause 2, which states:
“The privilege of the writ of habeas corpus shall not be suspended, unless when in cases of rebellion or invasion the public safety may require it”
Read into it, you learn more that way.
OK, what "Rebellion or Invasion"? Wouldn't the authorities want a militia, i.e. armed, able bodied civilians, to form in either event?