Unfortunately, not so simple. Elements of socialism are present in nearly every government ideology today. EU is outright socialist. Some programs of the US government are quite socialist (Obamacare as one example).
So it is just not possible to condemn the nationalism/socialism combination without condemning nationalism in general!
Yet worse, nationalism can be quite ugly without any detectable traces of socialism. Examples are plenty.
Just because NSDAP called itself both nationalist and socialist has very little significance, names of political parties are rarely meaningful. The two use parties have identical names (simply one prefers Greek and the other Latin) and neither stand for democracy aka republic, but rather for oligarchy!
Nationalism by itself is no danger, in spite of the recent false definition being promulgated of it being the belief that one’s own nation is superior to others.
The left conflates it with jingoism, for the purpose of pushing its own internationalist agenda of “abolish(ing) countries and nationality” (take note). Nothing wrong with national anthems and flags, and the like.