Who said anything about an immutable constitution?
I was under the impression that the US constitution was immutable.
You are saying that one geographic areas majority counts as a democracy. Well other geographic areas would disagree. ... At the end of the day you need to balance the concerns and it's hard to balance concerns that you refuse to acknowledge.
Uh... foreign relations? That's not democracy either. What? I swear your argument changes every time I address it.
If the decision in question is between two countries (or one country and an unintegrated territory, in this case), the democratic way is to have both countries run a referendum and go through with whatever they agree upon.
Obviously this is really inefficient so we just use an elected foreign minister or whatever to negotiate and then ratify it later, which is less democratic but 90% of the time the effects are small enough that it doesn't really matter that much.
In the Puerto Rico case, we know that they want to be integrated as a state. We don't really have a good handle on what the average American thinks, because apparently referendums are too hard to organise there. Which means the responsibility falls to the elected officials - Congress - who are refusing to address the issue. In other words, they're refusing to address the concerns of people they are called to represent.
Now you might argue that no, Congress doesn't represent Puerto Rico because Puerto Ricans don't get to vote. That makes the whole thing even more undemocratic. They're not getting representation because representation is denied to them, and representation is pretty darn important when it comes to a representative democracy.