For one it goes with the territory. When designing a language you need to emphasize its strong points and Clojure's strong point is its (sane) dynamic nature an

For one it goes with the territory. When designing a language you need to emphasize its strong points and Clojure's strong point is its (sane) dynamic nature and they are playing to its strengths for example in solutions such as their Transducers. I don't view it as trolling. The mentality and style in dynamic languages are simply different. Once you add static typing, you break that mentality, replacing it with something different. Not inferior, just different. The patterns, the solutions end up looking different. This is why static typing added to a LISP like Clojure can only be optional and probably less powerful than what you can get with something like Haskell. Or in other words, type systems are not practical for Clojure. There are attempts, like core.typed. Such solutions don't work very well because as said, adding types changes what you're allowed to do, even if those types are optional. So he's speaking primarily in the context of Clojure. Also, poking fun at your competition is good marketing. People love it :-P