Is it just religious believers who look for ethical concrete?
Not at all, secularists often do too. There is, for example, an increasingly fashionable claim that science will decide which values are good and which are bad. I’m as critical of the false certainties of a morality rooted in science as I am of the false certainties of a divinely sanctified moral code. The desire to set moral values in ethical concrete is a yearning for moral certainty – a fear that without external authority, humans will fall into the morass of moral relativism. But there can be no getting away from the fact that as humans we have to stand on our own feet, think for ourselves, create our values and practices, and bear responsibility for them.
Isaiah Berlin felt similarly about his political principles:
Indeed, the only defence he offered of liberty's priority in politics was in terms of pluralism. If values were in conflict, then liberty's priority was procedural. A regime of negative freedom was the best guarantee of the public discussion of choices that a free social life required. But this left the justification of liberty trapped in a circle: freedom was required to make freedom possible. He never professed to be bothered by his own failure to ground the defence of liberty on ultimate principles. He tartly suggested that secular rationalists who sought unassailable guarantees for political principles were succumbing, without realising it, to nostalgia for the kinds of consolations once offered by religious faith. Berlin dismissed the very idea of seeking ultimate guarantees at all. "Principles are not less sacred because their duration cannot be guaranteed."