I think his point is that a lot of the alarmism seriously damages the ability for AGW proponents to reach people. Cities are quite fluid creatures, and as long as the seal level rise doesn't make specific sections of land uninhabitable overnight but rather in a 10-20 year period, we can plan for it and react timely. Of course, this doesn't account for problems like the severe weather you mentioned and a Katrina-level event, but we have completely different systems in place to deal with the more severe changes associated with them ("National Emergeny", aid injections, etc).
There's a lot of people who aren't deniers that anything is happening, but just don't see a reasonable solution available that would prevent the problems we anticipate happening. Our global society is simply too fragmented to apply and enforce a stop or reduction in CO2 PPM. So, we focus on damage prevention rather than problem prevention - what technical solutions can we come up with over the next 30 years that might make this problem, not a problem at all. Or, what problems are something we can adapt to on a normal time scale with our current setups. This latter category is one that I and many others think the "sea level rise" problem falls into, and feel that people terrified of New York City magically being underwater in 100 years drastically underestimates human ingenuity.