"For in the theoretical field bourgeois economics no longer engages in blithe and joyous fights"

This quote by Rudolf Hilferding is referring to the field of bourgeois economics, which is a branch of economics that focuses on the financial activities of the middle class. Hilferding is recommending that in this field, there is no longer any enthusiasm or happiness in the debates and conversations that take place. This might be due to the truth that the theories and ideas that are being gone over have become more complex and tough to comprehend, or that the disputes have ended up being more heated and controversial. It could also be that the arguments have become more concentrated on the practical implications of the theories, rather than the theoretical elements. Whatever the reason, Hilferding is recommending that the arguments in the field of bourgeois economics have actually ended up being less enjoyable and more serious.