Much of entertainment that is marked as supposedly for “mature audiences only” is reflective rather of an immature mindset, i.e., an obsession with graphic violence and sexual imagery is conducive not to mature thinking on matters but rather to tawdry and sensationalistic presentations.
Instead of a “Warning: mature content” it should rather read “Warning: juvenile content”. The rise of sexual imagery and graphic violence in various entertainment products is part of a larger trend towards juvenile behaviour and thought-patterns on the part of supposed adults in society.
In this sense, “mature content” is a joke. Once you get that it is really immature, you can dismiss the explicit or implicit claims made by it for what they really are (unfortunately, one cannot dismiss its impact).