What makes Lisp...Lisp?

If you starting removing features from Lisp, at what point is it no longer Lisp? Some people claim Clojure shouldn't be considered a Lisp. Is it because too much Lisp was removed?

What is at the very heart of Lisp that makes it Lisp?

>>20
Enjoy writing programs which are hundreds of times longer than they need to be, and a lot less robust. Current CL compilers are pretty damn good, so speed isn't really an issue, and if something is too slow, optimization isn't that hard, in the worst case scenario, you just use the FFI.