Alright, I'll take the first billet: it obviously depends. Because they aren't being allowed to vote and participate in their government? Absolutely. Because they're nervous the enslavement of human beings is about to be upended? Nope.
Pretty much this. Generally speaking, I see government as a contract between the people of a given nation-state, not as a contract between various geographic subdivisions of that state. This leads me to oppose secession in most cases, except when consented to by both parties as opposed to just the seceders, or when the central government has
de facto annulled the contract by denying the applicable state/region representation.