Amen. I was irked by the "purity" factor as well. Adam's (ato's) response in the comments is dead on: "I needed an Atomic counter. Java has one. I used it."

One of the biggest draws of Clojure is that it runs on the JVM so you get access to Java's libraries. It is baffling to me how someone could describe using Java via Clojure as being a no-no.