Psychologists warned that the decision could discourage people from having children in a country whose birthrate is already one of the lowest in the world, while commentators said it could boost Italy's already high unemployment rate.
The case revolves around a wealthy family in the southern city of Naples, where the father is still paying some $680 a month in maintenance to a son who is in his 30s and has a university law degree.
The son also has a trust fund worth some 250,000 euros, lives in one of the smartest parts of the city, and has turned down several job offers.
But the court ruled that the father, Giuseppe Andreoli, who is a former parliamentarian and a respected Neapolitan medic, should carry on supporting his estranged son. "You cannot blame a young person, particularly from a well-off family, who refuses a job that does not fit his aspirations. The parents have to pay for their upkeep," said the court in a verdict handed down earlier this week.
Andreoli said on Friday he was shocked by the decision.
"I feel disgust for a country that I love. It wasn't always like this," he told Reuters.
The ruling struck a chord in Italy where almost one in three people aged between 30 and 34 still live with their parents, preferring home comforts and mothers' cooking to the challenge of striking out alone.
"This decision sets a dangerous precedent," said psychologist Gianna Schelotto. "Up until the 1980s, young people wanted emancipation from their families even if it meant going out and cleaning dishes. Today, 30-year-olds still feel young and aren't prepared to make sacrifices."
The growing reluctance to cut the apron strings has coincided with a falling birthrate, now put at less than 1.2 children per woman -- the lowest level in Italian history.
"Italy is faced by a deep cultural problem. Young people enjoy a great quality of life and enormous freedom by staying at home. Without enormous incentives, why should they leave?" said Riccardo Grassi, who works for the Milan IARD research institute which specializes in youth issues.
The problem is compounded by the fact that it often takes years to complete a university degree in Italy, graduates' starting salaries tend to be low and, unlike elsewhere in
Europe, the government offers little financial help to young parents.
Laborr Minister Roberto Maroni said on Thursday he was drafting a bill to offer tax cuts to newly-weds with an eye to boosting the birthrate.
But social commentators said the appeals' court ruling went in the opposite direction and would encourage children to stay at home rather than go out and find a job or start a family.
"Without seeking to, this (ruling) represents a pernicious obstacle to matrimony, which is essential to an ordered society and to the reproduction of the race," Rome's Il Messaggero newspaper thundered on Friday.