When people on the left use the term "materialism", they can mean many different things - but one important resonance is the Marxist one: the thesis that ideas circulating in the social field are 'determined in the last instance' by relations of production. In other words, norms, ideals, imperatives, identities and so on are ideological - they mystify the populace and serve the end of profit. So "matter" - the self-reproduction of capital - is prior to "thought" - ideology.
This notion can be (and has been) expanded to include not just positive beliefs and convictions (say in a particular religious doctrine or in bourgeoise liberal humanitarianism), but our very phenomenological horizon, the limits of what can be felt, conceived, experienced as given in even the most inchoate, ineffable way. This expansion represents both a radicalization of capital's power over human life and a radicalization within the philosophical tradition. It really is the case, if you think about it, that one's very drives, desires, presuppositions, habits of nutrition and so forth are mediated by the profit machine.
The argument goes that this includes, and perhaps especially includes, the experience of being free. Self-expression and affirmation of otherness on Instragram, for example, refreshing likes while transgressing norms, would in this theory be something like crown jewel of capitalist domination of hearts and minds.
I think it is here that there is a deadlock between philosophy's contemporary emancipatory horizon and those of both fine art and underground music. In art and music, social media has been accepted wholesale as a valid mode of promotion and medium for artistic practice itself, and there is no hotter topic that affirmation of polymorphous cultural, gender and sexual norms.
A sincere materialist philosopher doesn't quite know what to do with this - Zizek's many recent gaffes about gender identity are emblematic of this. For him, public focus on LGBT rights is a sort of regrettable "political correctness", a manifestation of Nietzsche's "last man" who withers away, unable to make subjectively embodied choices, or Hegel's "beautiful soul", railing emotionally against a system with which she is basically complicit in her lifestyle.
There is something to this critique, which I think in one way or another we all felt upon the election of trump: realizing we had been merely spouting cute, curated views in a Facebook echo chamber and so forth while doing little or nothing to actually engage (even discursively) the actual core antagonism of our time. On the other hand, there is something to the obvious critique of the privileged white male who associates the struggle for, say, transgender rights or respect towards cultural heritage with a sort of needlessly permissive / PC outlook, while continuing to go on enjoying his privileged white male status.
I guess what I mean is that a lot could be done to define exactly what it is we are still hoping to save from the tentacles of 'world-capitalism'. In a way the answer is obvious: it is always egalitarianism, the equal opportunity for all to live, work and express autonomously. But the arts are tragically far away from being coordinated with respect to actually enacting this.