Rationale (July, 2009):

The current treatment is sufficiently useful to warrant the inconsistency with the other handling of access control. In particular, it enables such cases to be detected by SFINAE.

An implicitly-declared special member function is defined as deleted (11.4.5 [class.ctor] paragraph 5, 11.4.7 [class.dtor] paragraph 3, 11.4.5.3 [class.copy.ctor] paragraphs 5 and 10) if any of the corresponding functions it would call from base classes is inaccessible. This is inconsistent with the treatment of access control in overload resolution and template argument deduction, where accessibility is ignored (but may result in an ill-formed program). This should be made consistent.