It means installing a big runtime they aren't familiar with, and getting their feet wet with a huge ecosystem which spans from weird stacktraces to the standard libraries and beyond, and is associated (somehow wrongly) with boring code and old enterprise solutions.
Clojure stack traces are usually long and somewhat leaky, they are hard to read without (and sometimes even with) preexisting knowledge about Java / JVM / Clojure implementation details.
On the other hand, with some Java/JVM knowledge, they are very helpful. Whenever I come across supposedly nice error messages in most other languages, I'm convinced more and more that stacktraces are one of the right ways to do it...
Actually that is not true, Ruby stack traces are beautiful. Recently i saw a feature called "Did you Mean?" Have you ever seen such a stack trace in any other language? Clojures Stack traces are unreadable. My strategy with clojure debugging is usually commenting code and println thats how bad stack traces are in clojure but the thing is Clojure as a language is very thoughtful and thought provoking much more than any scheme i have seen. And certainly more enjoyable to code in than Ruby.
Folks at-least comment with a good reason before giving negative points for a comment. It helps clarify how the message was received a negative point without a comment is quite pointless and banal.