what are the disadvantages of "friend class" in C++ design patterns? [closed]

There are many advantages of using friend class to increase abstraction and encapsulation of a library. What are the disadvantages of "friend class" in C++/Java? There is a opinion that friend class violates encapsulation, but I feel its quite opposite, friends increase encapsulation.

https://isocpp.org/wiki/faq/friends

Any thoughts why "friend class" should be prohibited?