The whole point of secession, whether in the US, or Catalonia, or in China[1], is that you have reached a point where you are
not able to come to a bilateral compromise on issues that affect you.
If you need bilateral support to exercise your right to self-determination, you don't actually, in practice, have any right to self-determination.
It's like saying that you have the freedom to leave your abusive job, but only as long as your boss lets you quit. That's not freedom, that's slavery.
[1] And yes, I am aware that the case in Scotland was a bit different. Props to the UK for being, as an outside observer, reasonable about the whole affair.
