From a fan and student of Miyazaki-san:
"Porco Rosso" is the master's most autobiographical work, for once he was not trying to impart any moral or environmental lessons to children or young girls or the Japanese society, as most of his other works did---but a heartfelt fantasy projection of himself (being an independent agent neither belonging to your typical Japanese Anime Industry or the Hollywood/Disney American Culture juggernaut, as symbolized by the brash American Pilot-Fighter, Curtis).
It's also a celebration of his fellow frustrated romantic and idealistic adults (many tired Japanese salary men and animators) who have not completely surrendered their youthful dreams to the MAN/military industry.
Set in Post WWI Europe, where Fascism was on the rise, the Continental world it captured was a last breath of fantastic and natural freedom before a long darkness set in...
The genius stroke here is by turning the protagonist into a PIG, a whimsical yet literal mockery on those old-fashioned/outdated all-male/brotherhood chauvinist melodramatic adventure genre it so lovingly appropriates, and a gentle dig on "mankind" in general, all in good and slightly surreal fun.
In this story, Miyazaki made fun (instead of preaching to) of his society, himself and his prominent role in it.
Yet, behind all the cartoony surface lies the touching elegiac sadness of a lost past and a yearning hope (placed esp. on a young female) for a better future, straight from Miyazaki-san's cynical/sentimental heart.
Presented as a light-hearted lark only makes its immersing nostalgia and lyricism all the more spontaneously enchanting
and unexpectedly affecting. A magical paradox of his great art.
"Porco Rosso" is the "Casablanca" of cartoons with a touch of Roald Dahl, and the most under-rated and overlooked of Miyazaki's fabulous work.