I'm not sure why there was so much controversy over it. It was explicitly anicipated in the Federalist Papers, and Article III, Section 2 states, "The judicial Power shall extend to all Cases, in Law and Equity, arising under this Constitution...." Elsewhere, it states that the Constitution itself is indeed law ("the supreme Law of the Land"), so therefore the courts clearly have the power to apply it, as they would any other federal law.
None of our branches can perform its function without making factual determinations. How can the Congress be expected to appropriate funds for the construction of a new post office in your city without first making the factual determination that a new post office is needed?
Congress can make factual determinations to do what they have the power to do. In the case of enforcing the 15th amendment, they have the power, as I said in the previous post, to appoint the officers and define the procedures for dealing with the lawbreakers. Information that they might need in order to pass such legislation would include: the number of polling places throughout the country, particularly in the areas where compliance is likely to be a problem; the success or failure which current procedures have had in ensuring compliance; the tactics that lawbreakers use in order to cover their activities - these are things that would help determine how much funding is needed to support the authorities, what agencies they should be allowed to share information with, what their command structure should be, and what the consequences should be for violating the law. They do not need to make investigations to determine what kinds of additional practices should be outlawed, because they don't have the power to outlaw them in the first place.
And if there already exists two post offices within one block of your home and the Congress decides to build another post office on your block, do you think that the judicial branch has the power to decide that the Congress is mistaken in its factual determination that the third post office is necessary?
No, of course not. If Congress is given the power to establish post offices, they can establish as many as they damn well please. In the case of outlawing literacy tests, the issue isn't whether or not Congress' facts are correct, because that's irrelevant. The only issue is whether or not they have the power to outlaw such tests to begin with, which they don't.
If the Congress makes the factual determination that certain states are using literacy tests to deny or abridge the right of citizens to vote based on their race and that it is necessary to suspend the literacy tests in order to enforce the Fifteenth Amendment, what legitimate procedures exist for the Court to determine that the Congress's factual determinations are incorrect?
It is not necessary, and certainly not proper, by any stretch, to suspend a lawful practice in order to enforce an unlawful practice. As I mentioned, the authorities go after businesses all the time for violations of anti-discrimination laws, without there being any need for suspending the use of the ordinary criteria business use to screen employees, regardless of whether or not some businesses have been dishonestly applying those criteria in a discriminatory manner. It's no different with screening of voters. States have the right, under the Constitution, to use whatever screening criteria they choose, except for race, color, previous condition of servitude, gender, payment of poll taxes, and age, for those over 18. Everything else is fair game, and indeed protected by the Constitution from congressional interference. The only thing the federal authorities have the power to do is take action against specific violators, or suspected violators, when they've determined that there have been, or are likely to have been, violations of the rules I mentioned above.
Well, believe it or not, there were some in those days (including President Jefferson) who believed that the Supreme Court had not been empowered by the Constitution to tell the Congress that the Congress had incorrectly interpreted the Constitution when it enacted legislation. They argued in substance that courts were supposed to just read and apply the laws of Congress and that courts were not supposed to make the laws. As a matter of fact, I still hear politicians and others making that argument.
But Chief Justice Marshall agreed with you and held, "It is emphatically the province and duty of the judicial department to say what the law [including the Constitution] is." Marbury v. Madison (1803). And to give you an idea of just how talented Marshall was, he declared this power of judicial review in a case in which (1) the result was in favor of the Jefferson administration and (2) the result brought the litigation to an irreversible end. So there was nothing that Jefferson or anyone else could do about it.
Here's a part of Article I, Section 8 that I hadn't before mentioned:
"The Congress shall have Power . . . To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof."
In McCulloch v. Maryland (1819), the Supreme Court had an opportunity to provide some meaning to that provision. See if you agree with Chief Justice Marshall's reasoning in this case:
"The government which has a right to do an act, and has the duty of performing that act, must, according to the dictates of reason, be allowed to select the means, and those who contend that it may not select any appropriate means, that one particular mode of effecting the object is excepted, take upon themselves the burden of establishing that exception."
If you agree with Chief Justice Marshall's reasoning in McCulloch, who gets to select the particular means by which the Fifteenth Amendment is to be enforced? And who would have the burden of establishing that the means selected (i.e., the suspension of literacy tests) is an improper means of enforcing the Fifteenth Amendment?