In After Virtue Alasdair MacIntyre makes the argument that because modernity lost its story, to use the words of Robert Jenson, we lack a coherent moral vision of our common life together. What we have, instead, are bits and pieces of a variety of incomplete and rival ethical systems. We have lots of different ways of defining "the good" but no clear way to adjudicate between these goods when they come into conflict.
Here's the outcome of this situation.
First, modern political discourse repeatedly brings rival goods into conflict. For example, in the abortion debates protecting life (a good thing) is pitted against the right to make decisions about your own body (a good thing). Two goods pitted against each other.
Regarding the debates about refugees and immigration, a concern over caring for the vulnerable (a good thing) is pitted against a concern for safety (a good thing). Two goods pitted against each other.
The examples abound. Pick any political controversy and you'll eventually find two goods pitted against each other.
Since we lack the ability to adjudicate between these goods we're forced to making one good triumph over the other good. This is difficult to do because these are obvious goods. Evidence for the goodness of the goods is clear and unimpeachable, so it's impossible to convince people that a good isn't a good.
It might be argued that a democratic process could help us find compromises between these rival goods.
That democracy is increasingly unable to bring about these compromises is because when two rival goods repeatedly compete in the public sphere the desire to have one good triumph over the other good causes the parties advocating a good to trivialize, demean, and diminish the rival good.
Democracy, thus, leads to the demonization of the good, making compromise and civic discourse increasingly impossible. Instead of a compromise between two rival goods, the political fight is transformed into Good versus Evil.
At this point, when good is called evil, democracy is doomed.
Calling the good evil, to use biblical imagery, is blasphemy against the Holy Spirit, the unforgivable sin. It signals that our moral compass has been damaged beyond all recognition, and now nothing stands between us and the abyss.