Can any state or states leave the United States at any time for any reason?
Yes or No.
Yes, so long as it is done with the consent of the other states.
What do I win?
I have already answered that....of course the answer is yes, it is the question of the mechanics of secession that needs to be addressed.
The south was wrong in it’s methods.
For one thing there was never a vote by the populace of the south on the issue, and I use the term populace to include those that were slaves, especially since the south wanted them counted as full citizens when determining the number of vote and seats they got in the congress.
Secondly there was never any real attempt by the south to reach an agreement on the issues that lead to secession.
Thirdly Can any sovereign nation or state join the United States?
The answer is of course yes but there a specific process by which they can join for one the citizens of that nation or state must vote on joining the United States and secondly the congress of the United States must vote to admit them into the United States.
You refuse to admit that the same sort of process applies to secession.