A very simple argument.
The divide between leftists and conservatives comes down to an irreconcilable disagreement about the meaning of fairness with respect to the distribution of resources. Both camps basically agree that resources are fairly distributed when they are distributed in a manner such as that resources are allocated to where they are best utilized. For leftists, this means resources are most fairly distributed when they are distributed to those who need them the most--the bottom tier. For conservatives, this means resources are most fairly distributed when they are distributed to those who deserve them the most--the top tier.
This disagreement is irreconcilable because one position is neither commensurable with nor reducible to the other. This will inevitably lead to conflict, and the responsible choice for a person rightly belonging to either camp is to try to cause their side to be victorious in this conflict because this result will lead to what they believe to be a just and fair distribution of societal resources. All the rest is strategy and war. Please note that this does not necessarily mean violent confrontation. It merely means a conflict over who gets to legitimately use the engines of state to distribute resources in some particular way, and prevailing in violent confrontation is not a necessary condition for earning legitimacy in this sense when one lives in a society with predominantly civilized people. This conflict could be nothing more than trying to mean the public argument by rational appeal.
The problem with liberals is that they are not acting responsibly. Each person who is not suffering from a political schizoid syndrome is either a leftist or a conservative (though I suppose someone could truly be a centrist if they believe resources are fairly distributed by the Gaussian distribution). Postmodern liberals’ commitment is to conflict avoidance and creating an environment of freedom from harassment is perfectly suited for mastering identity politics for political advantage. This is a pragmatic position, because we live in a political milieu in which negotiated settlements to distributional conflicts are structurally imposed—i.e. some form of parliamentary democracy. So, an inclination toward deal making and giving up on one’s position to some degree in order to avoid conflict and reach agreement is rational within this framework.
But pragmatism aside, it is still irresponsible to avoid conflict when it involves sacrificing deeply held values about the nature of justice and fairness. Liberals like Clinton and Obama have shown that they are not committed to prevailing over rightists in the fundamental conflict over how resources are fairly distributed. And over the course of their tenures as president, they have presided over the continued concentration of wealth and privilege at the top of the income distribution, a predictable outcome in the face of a determined and highly organized cohort of rightists who are still authentically committed to their position. Liberals are not leftists, they are conservative enablers.
Postmodern liberalism has as its goal freedom from harassment. But not all forms of harassment; freedom from harassment of a particular kind. Postmodern liberalism has the tenous position, quite hard to balance, that sociological propositions for the broad categorization of groups of people are legitimate for the construction of both personal narratives and meta-narratives, but illegitimate for the construction of criticisms. So, people, as they are resting in the breast of these sociological propositions, should not be harassed by pejorative labels. The use of labels for the construction of a personal identity is fine, and this identity should rightfully be validated in this view. But harassment is out of the question, and outsiders, especially disinterested patrician reformers, need to be careful about how these demographic categorizations are used because any insensitivity could be a sign of insouciance and harassment. Data about people which uses these sociological categorizations as data labels is perfectly alright to mine by outsiders for the interpretation of patterns of public opinion, however. This makes for a great identity politician, but not for a goal-directed moral opponent of the concentration of material resources.