Both Carl and Robin presume that brain emulations will be economically significant - which seems very unlikely. We may eventually be able to back up minds, but by then we will have intelligent machines by other means that will be doing most of civilisation's cognitive work.
Carl's section about "unrestrained Malthusian competition" seems rather paranoid. It exhibits "cold-war"-era thinking. Advanced organisms are much more likely to trade with one another - which seems relatively unlikely to result in existential risk.
Both parties avoid discussion of what will probably determine whether such a single large entity forms or not - a cosmic monopolies and mergers commission. Robin presumably thinks such a thing will be unnecessary - on the grounds that coordination is so hard. Why Carl doesn't discuss it is less obvious. Perhaps he thinks it is obviously a product of a primitive political system. Today, some political thinking suggests that preventing large-scale cooperation is desirable, and that deliberate fragmentation is the way to go. If that perspective continues to dominate, it seems relatively unlikely that a unified system will arise - since the monopolies and mergers commission would destroy any such unity.
I don't presume that brain emulation will come first and be significant, and indeed think that it probably won't. The paper explored some issues relevant conditional on that turning out to happen anyway, including some that can be generalized to non brain emulation scenarios.
Regarding Malthusian competition, check out "burning the cosmic commons".
The monopolies commission you describe would be a singleton under Bostrom's account, capable of overcoming any local challenge to its authority.
Shulman on Superorgs
Best to read the link first and my comments later.
I have very little to comment on the topic itself, but I do find it odd that Robin takes such a confrontational stance, beginning from the first sentence "It has come to my attention that some think that by now I should have commented on Carl Shulman’s em paper" and culminating with a harsh analysis not only of Carl's conclusions, but about what (Robin believes) made him want to reach those conclusions, as well as SIAI's mission statement in general. There is negative framing, "obsession with making a god to rule us all (well)", that I wouldn't expect from someone trying to honestly represent the other side. It's not that I don't share some of those concerns, but to psychoanalyse (who you seem to have identified as) your opponent in an obvious effort to discredit, is at the very least unfair. I was generally aware that there was some kind of tension between the former dynamic duo of Hanson - Yudkowsky, but it seems to have become full-blown hostility.
Robin does seem to find the courage to say he's glad others are looking into emulations, but the overall vibe I get is of someone protective of a research field they believe they uniquely 'get', someone who feels others should just get in line or get out of the ring, and it's a vibe not uncommon in academia.