And that's where you are completely wrong because you're tying together things that are not related that closely. Tell us this, which UC law has been found to be unconstitutional? You are no more credible in making that claim than you would be if you claimed laws forbidding you from parking in a handicapped space are unconstitutional.
Now, please explain why you believe the "controlling law is employment at the will of either party". Why does that principle control the principle that you can be compensated for being laid off but not for quitting a job?
Your whole premise revolves around the assumption that all laws enacted must be necessary and proper and good instead of just plain wrong. Black codes were wrong, and so was the Dred Scott decision.
Simply requiring for-cause criteria is repugnant to the whole and entire concept of employment at the Will of Either party. It is a self-evident Truth.
Simply because States are forbidden to impair in the obligation of contracts. At-will employment is a contractual obligation between the parties involved. There is no requirement to work or hire. Unemployment compensation is simply compensation for being unemployed under a truer and more effective understanding of the law.