Right, but if Docker allows us to package much more complicated applications (as opposed to being forced to simplify) that gives the bugs more room to hide and

Right, but if Docker allows us to package much more complicated applications (as opposed to being forced to simplify) that gives the bugs more room to hide and increases the risk of unforeseen interactions resulting in security bugs in the application. So what I'm trying to say is that making complicated applications easier to deploy doesn't seem like a win unless you also mitigate the increased security risk that comes with more complicated applications.