Like I said, there are methods to determine these things. I'm not an expert in how independence referendums are carried out, but I do know that methods to determine whether or not people are eligible to vote in such referendums already exist and have been applied elsewhere in the world. So you're basically trying to make an argument out of nothing.
As for the Syrians, they have a right to determine things via referendums as well.
I believe in all people's right to self-determination. Self-determination is an internationally recognized human right.
All peoples deserve to have basic human rights, freedom, civil liberties, self-determination, etc.