I think there's a lot of truth in this. While we could build large arcologies today, with our current tech, I'm far from certain that we could deal with fires or other seriously problems in any fashion that wouldn't leave open the possibility of mass death on a scale never seen in a conventional city (or at least any conventional city that wasn't carpet bombed). Of course, there are also social factors at work - an arcology could be a wondrous city of the future, or it could become a giant Cabrini Green, which is a rather horrifying possibility, and it's far from clear how we could definitely avoid that possibility.

In any case, in UTGM, I can easily see Lifemaker designed living arcologies, which would make the idea of living in one exceedingly appealing - an arcology that grows up and eagerly awaits occupants (perhaps literally, depending upon the level of volition and intelligence of the city-brain) would be a very popular place indeed.