The sentence "The principle is, the farther from the scene of horror, the easier the talk." looks and sounds fine to me, but if I wrote it my internal editor would worry vaguely. To make things less vague here are some questions:
Is "the principle" the subject?
Is "is" the verb?
Are the phrases "the farther[...]" and "the easier[...]" adverb phrases or prepositional phrases or something else?