There is no line between a migrant and a refugee. People make rational decisions based on all the data they have. Almost everyone in the third world would be better off moving to the first world. If these billions of people were allowed to do so the first and third world quality of life would average out.
The current first world inhabitants would have a worse life and those from the third world a better life.
The belief in modernity which creates the first world wealth and stability would be watered down.
If Europeans want to keep there safe, stable, wealthy lifestyle they had better take the sugar off the table and wise up quickly.