I agree with all of this, with one caveat. If someone argues that we should base policy TODAY based on what the Founding Fathers thought when they were alive, then it IS appropriate to judge their beliefs in the context of today. Not in the sense of deciding whether the FF were “good” or not, but in the sense of deciding how much weight to give their opinions and beliefs.
Not sure whether you’re aware but “apoligists” refers to apologetics, not people apologizing.
What? No.
An apologist (which you appear to have misspelled) is generally defined this way:
a person who offers an argument in defense of something controversial:
Apologetics refers to a much more narrow philosophical (often theological) concept.
What is Apologetics? - Grace Theological Seminary - Christian Apologetics
You appear to be the one confused on word usage.
History is complicated. There were numerous residents of the purported Confederate States of America who were staunch Unionists. Some of these Unionists even enlisted in and fought for the Union army. Others formed or attempted to form alternate pro-Union state governments. And a few of them owned slaves!
I think several of the posters in this thread are conflating “constitutional or unconstitutional” with “right or wrong.” I think we would all agree that slavery is wrong. The original question has more to do with what were the constitutional powers of the U.S. president in the 1860s.
To add to all of this, we have the Corwin Amendment
No amendment shall be made to the Constitution which will authorize or give to Congress the power to abolish or interfere, within any State, with the domestic institutions thereof, including that of persons held to labor or service by the laws of said State.
Ignoring the fact for a moment that it was the President not Congress that issued the Emancipation Proclamation, if the Federal government couldn’t end slavery then why need a Constitutional Amendment?
Right when someone is called an apologist, it’s a reference to religious apologetics, not someone saying they’re sorry for something.
A president can invoke war powers in the case of a large insurrection as well as in a war against another recognized nation.
Article I for example notes that one of the reasons that Habeas Corpus can be suspended is “Rebellion”
That is one meaning, but not the only meaning.
There is a more general, non-theological meaning:
Sry if I’m being unclear but that’s I was trying to say - when people say apologist they’re using a general term that references religious apologetics specifically.
No, they aren’t. They are sometimes doing that. They are not always doing that. In fact in my experience most modern users of the word apologist aren’t using it to mean it in that way. That being said a lexical argument about a word isn’t the topic of this thread, so I’ll speak no further on the matter.
I mean reference the way 3 strike policy refers to baseball, mot to mean that all usage of the term is literally talking about baseball.
This would be a good question for Clarence to ask Ginni. 
Let’s go with your monarchy example. And let’s keep in mind we’re talking about how widely slavery was practiced. What exactly does it mean to practice slavery? Does my living within a hundred miles, or even a hundred yards, of someone who thinks they can (and allegedly does) own another person and their descendants mean that I myself am practicing slavery? I think not.
There is the institution of slavery, and there is the practice of slavery. Likewise, there is the monarchy as a system of government, and there are the actual monarchs. Monarchy, like the institution of slavery, might have been widespread throughout history (might), but actual monarchs and the actual practice of slavery were much more limited.
And, as noted, you have apparently missed what the word “apologetics” means, and also who exactly I am accusing of being an apologist.
The fact that you apparently get this definition leads me to wonder how you could possibly have missed my meaning.
And now just to bring it back around again to the OP. If I were to grant that it were even possible for one person to be the property of another, to the point that even the descendants of the alleged “property” would themselves be property, I could probably craft an argument to support the proposition that the Emancipation Proclamation was unconstitutional. Although that might be because I am viewing history through the lens of the equal protection clause, and of course the equal protection clause didn’t come around until the 14th amendment, so maybe it’s not so obviously unconstitutional after all.
But that’s only if I grant that people of recent African ancestry could in fact be owned as property under the Constitution. I can only imagine that to be the case if I also imagine that the Constitution would have permitted all those belonging to racial classes that are in every way equal to White Anglo Saxon Protestants (or Englishmen and their descendants in America as the founders might have said) could also be enslaved (and have their children be likewise born into slavery, in perpetuity). And if someone wants to make that argument—that the Constitution could have accommodated the enslavement of Thomas Jefferson and his descendants in perpetuity (I mean, except the descendants he had through the rape of a slave woman who could not meaningfully consent, that is), then okay. I guess it follows you could also make an argument that the Emancipation Proclamation was unconstitutional.
But I cannot seriously imagine that, were you to put the question to Thomas Jefferson or George Washington, “In America, under the Constitution, could anyone equal to a man of English descent, born in this country, be subjected to slavery as the people of Africa are by your own household?” that they would have said anything other than “Not only no, but hell no. No man who is the equal of an Englishman, now an American, could ever be a slave under the laws of this country.”
It is on that basis, my presumption that the founders would to a man have been anti-slavery for anyone who was equal to themselves, that I must therefore conclude that their allowance for African American slavery was based on an error in fact, and that under the law of the land—the Constitution—they could not actually be enslaved, and they were only permitted to be treated as enslaved by lawmakers for so long as that error of fact remained predominant (and likely would have continued on in such a state, but for the 13th amendment).
Now do the 3/5 compromise. Plug that in to your analysis.
And indentured servitude.
Are… are you trying to argue that slavery was never practiced in the United States?
I think they’re trying to say that it was all just a big misunderstanding.