Social patriots were more prone to nationalism. A rather sad example of this is the Marxist-Menshevik Georgy Plekhanov. After the war began, he stood up for Tsarist Russia even before any revolution. And about that he didn’t really use much of “Marxist arguments,” and even sometimes said horrifying things. I remember reading how he quarreled with German internationalists after the outbreak of the World War, because he told them at a meeting that “as a Russian, I can’t wait to see your German flesh on a Russian army bayonet!”
I guess in 1914 almost everyone in Europe went nuts