Answer: In Europe nationalism is considered very dangerous ideology because of its role in 19th-century and 20th-century wars (in Europe and elsewhere) and today can endanger project of European Union. That is why some politicians are afraid of it. At the same time it is true that nationalism is a part of European political history.
Explanation: European Union is a project built against local nationalism and that is why it tries to neutralize it. Nationalism is a part of extreme-right movements and parties that try to monopolize nationalist and patriotic discourse (including "European way of life"). Emmanuel Macron and other politicans are trying to keep nationalism at bay, marginalize it.