I suppose everything in the Constitution looks simple to someone who doesn't understand constitutional law. You completely ignore the all-important subject of which standard of review applies in a given case. A state law challenged on equal protection grounds is subject to strict scrutiny if it either involves a right the Court considers fundamental--e.g. voting--or makes a "suspect classifications"--i.e. singles out a certain class of people for disparate treatment. The first and most obvious suspect classification was blacks. The Court has extended this to any classification by race or national origin, but that's it. And the Sixth Circuit opinion made short work of the laughable argument that by calling marriage a fundamental right in Loving, Skinner, and even earlier decisions, it meant that to include same-sex marriages.
State laws that discriminate based on sex, intellectual disability, or legitimacy are subject to a form of heightened scrutiny that Court calls "intermediate review." With all other state laws, rational basis review applies. And contrary to what you claim, that level of review is deferential enough that it allows states to discriminate by law in all sorts of ways without violating the guarantees of either equal protection or due process. In marriage, for example, many states discriminate against cousins, let alone partners who are more closely related than that. Most, if not all, discriminate against people seventeen years old and younger. They all discriminate against against people who are already married, as well as people who want to marry more than one partner. Where is your outrage about the discrimination against those people? Why aren't those laws unconstitutional?
If Fourteenth Amendment equal protection and substantive due process were as simple as you'd like to think, there would not have been hundreds of law review articles and books written about them, nor would there be decades' worth of decisions by the Supreme Court establishing the complex rules about how they apply, to whom, what standard of review is called for, etc. The Sixth Circuit's opinion gives a good general overview of these issues, for anyone who would like to learn about them. People who latch onto simplistic explanations do so because like religious fanatics, they have already closed their minds to facts and reason.
