Especially for the relatively poor red states that depend on blue state subsidy.

There are still some southern states that have massive poverty. The union did not serve them well. I can see how they would be better off on their own. Hawaii as well. And its not just about poverty. Hawaiians would like to regain control over their culture, tourism levels, and so on. King of your castle. Even if your castle is just a shack. Counts for a lot. Also cities like Chicago and Detroit experienced huge declines, because of trade with China, that mostly benefits California. I can see how they would like their own policies on trade.

I'm sure there were people walking around saying that in 1775. Yet Greater good prevailed, and US got its independence from Britain. Since its a Democratic Union, I hope it can be dissolved in a democratic way. Is the worry that each state would have fight to get independence?

I am not a fan of histotical analogies like that. One very likely outcome of a U.S breakup is a global economic depression. Another one is Chinese hegemony. I am not a fan of either. Sure, it might work out alright. But it might not.