If you believe in rule by the people, secession needs to be a valid option. It's how America was founded, and it's more or less how Canada was founded. Now, using it as some sword of Damocles is harmful to society, but calling those who want to leave criminals isn't helpful. In the opinion of Quebec, 50% plus one is sufficient. Perhaps I don't agree with that, but I think it's the minimum that should be acceptable. But I think it's less of a crime to say the nation is no longer serving the will of some significant segment of the populace and that they wish to have the final say in their governance.

That said, capitulation to a foreign power at the expense of your nation is a different issue.