The link you provided did not talk about the reasons for secession. It was about the legality of it from an American Constitutional perspective. Look at the top rated comment of this discussion on history.stackexchange.com. [1]
Secession was about preservation of slavery. I don't think there exists a cogent contrary argument.
I think I agree with you on this point. The last answer attempts to provide some nuance but even at the root of those is...slavery.
I also think that I've seen a lot of rhetoric thrown around online and this is the first time I posted about it, so perhaps I was attempting to speak to the "flag symbolizes treason too" argument that you never made.
Secession was about preservation of slavery. I don't think there exists a cogent contrary argument.
[1] http://history.stackexchange.com/questions/553/why-did-the-s...