If you're coming from a bondage and discipline language like Java or C# with public, private and protected access modifiers, Python's "everything is public" approach can seem excessively open-minded.

The prevailing culture among Pythonistas is that "We"re all consenting adults here". In practice, the leading underscore convention has proven sufficient protection even in large and complex Python systems we have worked with. People know not to use these attributes directly, and in fact they tend not to. Like so many doctrines, lack of access modifiers is a much bigger problem in theory than in practice.