I'd be interested in a lecture on what you are talking about there.
Ok, you asked for it. Lol.
We start with the due process clause. It says, "No person shall ... be deprived of life, liberty, or property, without due process of law." It applies to the federal government through the Fifth Amendment and to the states through the Reconstruction-era Fourteenth Amendment.
If you read those words, it's clear that the clause is simply requiring that the government follow a fair and non-arbitrary process before it can take away someone's life, liberty, or property. It deals with the procedural rights of citizens. Nobody disputes that the clause requires this, though there are obviously differences of opinion about what is meant by "liberty" and what process is "due."
However, courts have also interpreted the due process clause to take powers away from government regardless of the process followed arguably to protect "fundamental rights." This interpretation is not supported by the text of the clause or by the history of the clause. (In fact, the very term "substantive due process" is an oxymoron.) It is simply a raw assertion of judicial power.
However, the biggest danger of the doctrine isn't that it is isn't supported by the text of the clause but that it is unlimited in scope and arbitrary in application. As I indicated, the doctrine is designed to enforce "fundamental rights." Well, what is a fundamental right? Some are believers that "fundamental rights" are those expressed in the Bill of Rights. Most justices on the Court over the years buy into the idea that fundamental rights are those that are "implicit in the concept of ordered liberty" (which includes some of what's in the Bill of Rights as well as other rights that the Court might pull out of its ***). Well, that is nothing but vague subjectivity. That can be anything a justice wants it to be, and if an issue doesn't fit cleanly into that, the issue can be re-framed to fit. The result is that the doctrine gives the Supreme Court the power to strike down any law it doesn't like and to do so completely unfettered by the written law, and sure enough, substantive due process is the doctrine the Court applies when it has no other tools in its shed.
Look at Roe v. Wade. The Court obviously wanted to legalize abortion, but it didn't have any clear authority to do that, which is why it turned to substantive due process. It couldn't with a straight face claim that the right to an abortion was fundamental. It knew how ridiculous that would sound, so instead, it came up with a more benevolent sounding "right to privacy." It then deemed the decision to terminate a pregnancy to be inherently private (even though it involves someone leaving her home and engaging in commerce with someone licensed by the government), and voila, it had its vehicle to legalize abortion nationwide.
