Although a critic of economic liberalism, Quack never joined any of the socialist currents, although he did attend the 1872 Congress of the International. Nor did he join any other political current: he felt related to liberals, in particular Cort van der Linden, but disliked their individualism; he admired socialists' ideals, but not what he considered their "breeding of mistrust and hate" as a means to realize them; his own ideals resembled social conservatism, but he was too much of a democrat to feel related to the conservatism practiced in the Netherlands. He has been described as a "cathedral socialist" with Saint-Simonist ideas. According to Ferdinand Domela Nieuwenhuis, with whom Quack exchanged some letters, Quack lacked either courage or drive, and with these qualities, he might have become "our Lassalle". Theory and practice were in a state of tension in Quack's life: during the 1903 railroad strikes, he was president of the board of the state railroad company and supported the firing of 11% of the company's personnel. In his memoir, he recalled this episode as "the most cruel page of the book of my life", but still defended the decision.