Your points are well-taken, but some people tend to extrapolate the testing issues with specific cases like the ones you're describing and apply that same ethos

Your points are well-taken, but some people tend to extrapolate the testing issues with specific cases like the ones you're describing and apply that same ethos to projects that can and should be unit tested, such as web applications. Manual testing and QA are great but cannot provide the sort of architectural guidance that unit testing provides. If a module is difficult to unit test, it will also be difficult to maintain. Manual testing will not readily provide those insights.