@evs, that is strange, it really shouldn't crash the whole OS! You can try running like this:
open Spine.app
---
args frameless
Is there anything in the spine.log file or OSX Console app? You could try to upgrade to 10.8 I guess, but I can't promise it will work better. Unfortunately all this stems from Apple changing how they support Java in 10.8, it's a horrible mess. Other apps like Minecraft are having the same issues. You seem to be suffering from the changes necessary to run on Java 7, even though you are using Java 6. 🙁
