[T]he looming threat of ecological catastrophe; the inappropriateness of private property rights for so-called “intellectual property”; the socio-ethical implications of new techno-scientific developments (especially in biogenetics); and, last but not least, new forms of apartheid, in the form of new walls and slums.
The first three antagonisms concern the domains of what political theorists Michael Hardt and Toni Negri call “commons” — the shared substance of our social being whose privatization is a violent act that should be resisted with violent means, if necessary (violence against private property, that is).
The commons of external nature are threatened by pollution and exploitation (from oil to forests and natural habitat itself); the commons of internal nature (the biogenetic inheritance of humanity) are threatened by technological interference; and the commons of culture — the socialized forms of “cognitive” capital, primarily language, our means of communication and education, but also the shared infrastructure of public transport, electricity, post, etc. — are privatized for profit. (If Bill Gates were to be allowed a monopoly, we would have reached the absurd situation in which a private individual would have owned the software texture of our basic network of communication.)
The slum-dwellers, by contrast, he casts as the outsiders to the political community that prevent us from softening the edges of the other three antagonisms by personal action. The slum-dwellers live in an effectively extra-legal position: shorn of effective police and fire protection, beset by crime, outside the "official" economy, and deprived of health and social security protection. Their position is a constant threat to the capitalist order, and can thus act as a catalyst to prevent orderly resolution of the other three.
* I should clarify that I don't necessarily agree with Zizek, but he is an important and interesting writer whose ideas are worth chewing over, no matter how radical they might seem.