Careful to qualify that. Sure developers should write unit tests for their code when possible. But they should not be the ones coming up with the acceptance t

Careful to qualify that. Sure developers should write unit tests for their code when possible. But they should not be the ones coming up with the acceptance tests (product owner) and doing all the testing of their work (QA). I've seen that argument several times "Why can't the developers test their work?" For the same reason professional writers have proofreaders, editors, translators, etc. Because it would be amateur not to have more than one pair of eyes and one brain looking at something. No matter how good those eyes/brain are, they'll miss things that would be obvious to someone else.