Castro's comments came in a long opinion piece carried by official media two days after Republican presidential hopefuls at a debate in Florida presented mostly hard-line stances on what to do about the Communist-run island, and even speculated as to what would happen to the 85-year-old revolutionary leader's soul when he dies.
Cuba has become an important issue as the candidates court Florida's influential Cuban-American community in an effort to win the biggest electoral prize so far in the primary season.
Castro said he always assumed the candidates would try to outdo each other on the issue of Cuba, but that he was nonetheless appalled by the level of debate.
"The selection of a Republican candidate for the presidency of this globalized and expansive empire is – and I mean this seriously – the greatest competition of idiocy and ignorance that has ever been," said the retired Cuban leader, who has dueled with 11 U.S. administrations since his 1959 revolution.
Castro also disputed international media accounts about the Jan. 19 death of Wilman Villar, a 31-year-old Cuban prisoner, saying the man was not a dissident and not on a 50-day hunger strike as human rights groups and the island's opposition claim.
Castro reiterated the government's contention that Villar was a common criminal sent to prison for domestic violence, and that he received the best medical attention possible. Washington and several European governments have condemned Cuba for his death, and Amnesty International says it was about to put Villar on a global list of prisoners of conscience.
Villar has become a cause celebre for opponents of the Cuban government, but he was not a well known figure, even among island dissidents, before his death.
Republican candidate Mitt Romney said during Monday's debate that Villar died "fighting for democracy" and that his death highlighted the need to remain firm on Cuba. Washington has maintained a near-50-year trade and travel embargo on Cuba.
When asked what he would do as president if he found out Castro had died, Romney said he would first "thank Heavens" that the bearded revolutionary had finally "returned to his maker," to which Gingrich replied "I don't think Fidel's going to meet his maker. I think he's going to go to the other place."
Castro didn't refer to the comments specifically in his opinion piece, saying that he was too busy with other things to waste any more time analyzing the Republican competition.