In the case of the land of the Louisiana Territory, the United States paid for the land. Do you believe that settlers on American territory have the right to take that territory away for the United States for the purpose of starting their own state or joining another nation?
Why are you on this forum?
I could ask the same thing about the people here who seem to think the United States is an occupying foreign nation. Or any number of others. If you haven't noticed, there is a pretty diverse mix of opinions here.
The feds had no right to invade their homes and the Southerners had no obligation to leave them.
If you actually read the Constitution, many of the rights in the Constitution are qualified rather than absolutely guaranteed (interestingly enough, the right to bear arms is not qualified), giving the government a process for infringing upon many of them. For example:
No Soldier shall, in time of peace be quartered in any house, without the consent of the Owner, nor in time of war, but in a manner to be prescribed by law.
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger; nor shall any person be subject for the same offence to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation.
Excessive bail shall not be required, nor excessive fines imposed, nor cruel and unusual punishments inflicted.
In other words, the Bill of Rights presents a lot rights protected through restrictions and not prohibitions. Look at the above rights in terms of what they do allow the Federal government to do.
The Federal government can quarter troops in someone's house against their will in time of war in a manner prescribed by law. Searches and seizures can happen so long as they are reasonable and warranted. A person can be held to answer for a capital crime if they are indicted by a Grand Jury. A person can be put in jeopardy of life or limb, but only once. A person can be deprived of life, liberty, or property through due process of law. Private property can be taken for public use with just compensation. Finally, bails can be required, fines can be imposed, and punishments inflicted so long as they are not excessive or cruel and unusual.
You may not like or agree with that scope of powers and that's fine. But it does suggest that the government has domain over citizens and their property and this goes back to well before secession.