Karl Popper, The Open Society and Its Enemies, vol. 2:
This, of course, is not the only argument against the idea of a rule of love. Loving a person means wishing to make him happy. (This, by the way, was Thomas Aquinas’ definition of love.) But of all political ideals, that of making people happy is perhaps the most dangerous one. It leads invariably to the attempt to impose our scale of ‘higher’ values upon others, in order to make them realize what seems to us of greatest importance for their happiness; in order, as it were, to save their souls. It leads to Utopianism and Romanticism. We all feel certain that everybody would be happy in the beautiful, the perfect community of our dreams. And no doubt, there would be heaven on earth if we could all love one another. But as I have said before (in chapter 9), the attempt to make heaven on earth invariably produces hell.