In the second half of the twentieth century there was either pessimism about or else just outright rejection of the ideal of “enlightenment,” a concept which could be characterized as the foundation for all discussion of politics in the modern era. “Enlightenment” as a Western European political concept, is essentially the idea that reason and rationality can show us the way toward social progress. That progress would be the result of ongoing dialogue. Democracy and other forms of government that allow for reasoned discussion and disagreement, which put the fewest impediments in the way of liberty and freedom of expression, are best according to that ideal, since they allow for the best chance of that development which depends upon free discussion.
Nevertheless, we can see actual and potential problems with liberty (gun control legislation or even the growth of fascism) and with freedom of speech (which seems to be subject to the influence of the media, or muted by political partisanship) present in our society and in modern history. The conclusion of some critics is that liberty is something too dangerous to be handed to the masses. There is too much potential for liberty to be manipulated in ways that lead the masses astray, sometimes with horrific results (e.g. the holocaust).
All this could very well make one think that the enlightenment project was misguided. I think a mistake was made in overestimating the extent to which we have actually developed. There is a distinction that must be made between knowing what is right and building that knowledge into a cultural norm that can be called true progress. In other words, the step from rational discussion to actual cultural changes, rooted in changes in actual human behavior, is much, much longer than the enlightenment philosophers expected.
The twentieth century bears witness to this: while to many people living at the start of the twentieth century authoritarianism, totalitarianism and fascist ideologies might have seemed obviously wrong, there were equally obviously the seeds for such developments in human nature which were allowed to grow and were exploited by open societies that permitted such growth. If true enlightenment was attained at the end of the twentieth century, it would be in the form of the establishment of new cultural norms that reject such ideals and have the effect of guiding everyday people away from such behavior in their private lives. It would amount to a shift in consciousness and behavior on a social level.
This seems like a nice attainment, but certainly runs very much counter to the optimism of the 17th and 18th centuries. It seems that we must wait to learn things culturally, adopt ideals as cultural norms, even if just about everyone agrees upon them. Despite the extent to which the 20th century has disappointed our sense of our own progress, in a sense, putting such things as unjust authoritarian behavior behind us though a revaluation of values would be a major accomplishment. Arguably, such things as the growth of truer forms of equality in the latter part of the 20th century and early 21st may have received some impetus by the growth of such consciousness; and again, what some perceive as fascist tendencies in Trump would not be so ruthlessly criticized were it not for the growth of such awareness.