The Supreme Court did not rule that powers granted under the Militia Act were unconstitutional. Section 1 of the Militia Act pertains to insurrection and repeats the application requirement of the Constitution, lifting the phrasing directly from the Constitution. Contrary to your misbegotten assertion to the contrary, when speaking to insurrection, the requirement is there in the most explicit language possible.
If your cockamamie assertion were true, Congress would have been amending the Constitution by legislation.
Read it again, the Militia Act of 1795 states "in case of an insurrection in any state, against the government thereof, it shall be lawful for the President of the United States, on application of the legislature of such state, or of the Executive, (when the legislature cannot be convened,) to call forth such number of the militia of any other state or states, as may be applied for, as he may judge sufficient to suppress such insurrection."
"That whenever the laws of the United States shall be opposed or the execution thereof obstructed, in any state, by combinations too powerful to be suppressed by the ordinary course of judicial proceedings, or by the powers vested in the marshals by this act, the same being notified to the President of the United States, by an associate justice or the district judge, it shall be lawful for the President of the United States to call forth the militia of such state to suppress such combinations, and to cause the laws to be duly executed. And if the militia of a state, where such combinations may happen, shall refuse, or be insufficient to suppress the same, it shall be lawful for the President, if the legislature of the United States be not in session, to call forth and employ such numbers of the militia of any other state or states most convenient thereto, as may be necessary, and the use of militia, so to be called forth, may be continued, if necessary, until the expiration of thirty days after the commencement of the ensuing session."
Further more, the Constitution states,
"The President shall be Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States; he may require the Opinion, in writing, of the principal Officer in each of the executive Departments, upon any Subject relating to the Duties of their respective Offices, and he shall have Power to grant Reprieves and Pardons for Offences against the United States, except in Cases of Impeachment.
Finally never forget what Thomas Jefferson once said,
"It is our duty still to endeavor to avoid war; but if it shall actually take place, no matter by whom brought on, we must defend ourselves. If our house be on fire, without inquiring whether it was fired from within or without, we must try to extinguish it."