AMUSING, INTERESTING, OUTRAGEOUS, or PROFOUND

It's more about stability. Yes, the piece of paper does not have any more authority than we choose to grant it, but giving credence to the law consistently lets people understand what to expect from society. They see it effectively determining people's behavior, and can feel safer so long as it looks out for their needs. In this way it acts as a stronger barrier to future bad behavior.

But when people are able to disregard the law when it doesn't seem like a big deal, it makes it easier for bad actors to circumvent it later on. A rule doesn't mean much when you just ignore it whenever it becomes inconvenient. One day it may just be slacking on a Miranda warning, but that can spiral into much larger trespasses on people's rights if the latter are no more illegal than the former. And so a threat to one part is a threat to the whole.

It's also worth pointing out that the law isn't expected to ever be perfect, or static. It should update to better reflect the values of society over time. And there are legal ways for people to avoid punishment even when they violate a law. A jury can refuse to convict a defendant. The president can pardon someone. Plea deals and prosecutor discretion can mean a charge is dropped. The convicted person can appeal a guilty verdict based on due process violations. A statute of limitations or other restriction can render them immune.

For Lincoln's blockade specifically, the Supreme Court ruled it as constitutional when it was challenged, and Congress later retroactively approved of it. So it was legal, based on the way we define what that means.