Fairly standard points, and I have tried to avoid broadly speaking making any particular arguments about economic socialism for these reasons, namely to avoid being bogged down.
Rent-seeking is a real issue in general, but I hope it's clear that there is relatively little scope for this for institutions designed predominantly to avoid international war. Institutions such as the UN and EU may be inefficient and sometimes act in perverse ways, but by and large they are not astonishingly expensive and have (arguably, but I will side with Pinker on this) largely prevented great power war for more than half a century. I think this is a completely different topic from economic regulation and I hope that you'll agree that at least as a minimum, institutions such as these both necessary and desirable for international peace. I'm not advocating North Korea here, I'm advocating an expansion of the scope of the existing, successful institutions in the prevention of global commons risks. The government doesn't have to control your thoughts, heaven forbid - but they do have to restrain you from nuclear war or unilateral geoengineering!
As for the self-regulation of economic activity, it seems to fly directly in the face of evidence to claim that letting individuals and corporations regulate themselves with regard to global risks has ever been effective in any way at all. The current crisis with regard to global warming, and long-term energy supply, illustrates this extremely well and it is very hard to see how anything other than international treaty can regulate such activities. Moreover on inequality, this is precisely and definitively what unregulated capitalism creates, and the current Piketty debate seems all the more remarkable because we've known this for two centuries now. If you don't want to create transhumanist inequalities, then wholly unrestrained markets are clearly a problem.
I'm very careful to avoid claiming anything about domestic politics because this really isn't the time or place and is a distraction from the topic of discussion. But in a broad sense, surely you agree that there is at least some minimal set of areas in which regulation is necessary beyond the familiar property rights. Existential threats such as great power war, resource depletion and climate change are things that we know full well cannot be addressed solely in terms of free markets, and regardless of the underlying economic system special consideration has to be given to these dangers as requiring international, independent oversight with the powers to police this.