Those sites are the sources of most of the canned quotes thrown up in lieu of argument here generally by those trying to defend the Insurrectionists of 1861.
My judgments are not limited to responses to small quotations. Nor do I consider myself that authoritative but when I see the same errors posted and reposted it gets tiresome in the extreme. One of the most egregious is the idea that since secession was not specifically forbidden it was allowed. This is like claiming that "divorce" should be mentioned in the marriage ceremony.
If the Constitution was so simple it would not have generated thousands of books trying to explain it. It is not and cannot be simple any more than the Bible could be.
As for the understanding of most people it is so limited as to be ludicrous. Even a site like this has people posting error after error which even non-experts can spot.
Oh, and perhaps you didn't know but the majority of the writers of the Constitution were lawyers. As were Jefferson, Hamilton, Adams, Madison, Monroe, Morris etc. etc.
There are two basic ways to interpret documents like the Constitution (and other laws).
The first, the Strict/Totalitarian method declares that anything which is not specificallty allowed under the law in question is forbidden. You tread dangerously close to this type of interpretation when you find limits on our state governments' sovereignty which are not specifically mentioned in the Constitution.
The other, liberal with a small "l", method declares "that which is not expressly forbidden is allowed".
A free society has no choice but to lean towards interpreting its laws in the small "l" liberal manner or it quickly becomes a non-free society.
Remember, the Constitution does not give us our rights, we already have those. The Constitution permits only those infringements upon our God-given rights as MUST be infringed in order for our government to perform its essential functions (and ONLY its essential functions).
So, from a Constitutional stand-point, that which is not specifically forbidden is allowed. Thus states' right to secede exists.
And since divorce is not specifically forbidden (at least under the laws of my state) it is allowed. It does not NEED to be mentioned in the marriage ceremony because it is allowed. As with secession, is it desirable? Not by me; but it IS allowed.