Well then to you, there's no need to justify succession. Depending on how fast you hold to that view, the rest here may or may not matter to you.
I used to see it that way was well. But I agree with the authors of the D of I, the part you stop just short of...
Prudence, indeed, will dictate that Governments long established should not be changed for light and causes; and accordingly all experience has shown, that mankind are more disposed to suffer, while evils are sufferable, than to right themselves by abolishing the forms to which they are accustomed."
Like other associations, the freedom to join doesn't necessarily mean you can justifiably leave anytime you want. The D of I was written to explain what it takes to justly "change" or "dissolve political bands".
Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes;
The reason I stopped short is because that next section adds nothing to the point. "Should not" is a suggestion, not a requirement.
Furthermore, your point ignores the fact that the Southern States did not consider their independence movement to be a consequence of "light and transient causes." They considered the issues separating the North and South to be quite serious and intractable.
Like other associations, the freedom to join doesn't necessarily mean you can justifiably leave anytime you want.
Associations like the Mafia perhaps, but I know of no legitimate association that says they will kill you if you try to leave.