>But agencies are political animals, subject to the whims of the current president, who can potentially change every four years. Courts are much slower to change, and much less vulnerable to the political whims of the current administration.
Kagan agrees that executive agents are more political and shorter-lived than judges. Which is part of why she dissented. A federal judge has no constituents, no chance for replacement if the will of the people is ignored. A bureaucrat is appointed by an elected President, so there's at least an indirect avenue for accountability by the people.
>If the law is ambiguous, courts must resolve the ambiguity.
If it's a matter of law, the courts did resolve disputes in step one of the Chevron deference system. Federal Judges are considered experts in law and Congressional actions. If the dispute falls outside of the legal framework (e.g., Kagan's examples of which new polymers count as proteins, or reasonable ways to return the sound level in a national Park to a near-natural state), then the judge went to step two of Chevron deference: defer to the subject-matter experts in the agency. It is ridiculous to expect a judge to get a crash course in hundreds of complex fields that could actually prepare him or her for an informed ruling. Deferring to the people who've studied and practiced the topics seems like the better choice.