In the first half of the talk he describes a "cultural capitalism" in which products you buy are supposed to also do some good in the world. He gives the examples of Starbucks and Tom's Shoes. He describes pretty well how it works, in negative terms, but doesn't actually give any arguments against it. That said, I do agree with him that "earn a lot, then give money away" does more to actually help people than "buy ethically, feel good that you are doing good".
It's the second half of the talk, however, where he starts giving his main argument, which is that helping people is bad. The idea is that we need a better system, and that trying to make things better for people within the current system is actively harmful in that it weakens the forces pushing us towards a better one. As a historical example, he says that "the worst slaveholders were those that were kind to their slaves" because that delayed the elimination of slavery.
While people who were repulsed by slavery had all sorts of examples of functioning non-slaveholding societies to emulate, it's not clear what we would replace capitalism with. Zizek acknowledges that 20th century communism was a "mega mega ethical, political, and economic catastrophe". So even if we let things get really bad, stopped all charity, maybe even did some intentional make-things-worse anticharity, I don't think that would lead us to something better. We'd just be letting more people suffer and die to no end.
Even if a better system is coming, however, does effective charity really delay it? If people don't get malaria, have more money, or grow up with fewer parasites are they any less empowered or motivated to change their situation for the better? If they are, is this effect very large? Large enough that your donation does more through indirect effects to delay the implementation of a better system than it does by direct effects to make people's lives better?
He argues against each major economic system, but just arguing that systems are bad isn't enough: we will have some system, and we need to pick among them. He gives no argument that we should do something other than stick to our current system, and he doesn't come anywhere near the question "if we want to make the world better, how should we go about it?".
(I previously wrote something similar as a comment.)