Well, I justify it by virtue of believing that my brain isn't some kind of abstract general-purpose thought-having or inferential-relationship-traversing device; it is a specific bit of machinery that evolved to perform specific functions in a particular environment, just like my digestive system, and I find it no more plausible that I can necessarily traverse an inferential relationship that an alien mind can traverse than that I can necessarily extract nutrients from a food source that an alien digestive system can digest.
How do you justify your assertion that I can necessarily traverse an inferential relationship if an alien mind is capable of traversing it?
Well, your brain isn't that, but its only a necessary but insufficient condition on your having thoughts. Understanding a language is both necessary and sufficient and a language actually is the device you describe. Your competance with your own language ensures the possibility of your traversal in another.
Here's the new thread for posting quotes, with the usual rules: