DC - I understand you're sentiment, but disagree for several reasons under certain circumstances -
1] Unpublished songwriters who actively shop songs to publishers, performers, managers, producers, et,al. should have the songs they pitch copyrighted. While most people in these professions are honest, ethical people, accidents do happen. Tapes and Cds get duplicated without the writer's name, address, etc.
2] People who are asked by publishers, managers, et.al to co-write with people who they don't know or know well. It's nice to have proof that Two-Chord Johnny really didn't write all that he claims to. This is probably the most commonly litigated issue in cases involving songwriting currently.
3] Anyone who performs their unpublished songs at songwriter showcases, writer's nights, open mikes, etc.
If you're writing songs to impress your wife or girlfriend or to have people pat you on the back, maybe a registered copyright isn't so important. But, if you're trying to make a living from your writing, copyright registration isn't such bad idea or a waste of $30.00.