"With one less murderer walking around, the rest of us can rest more easily," said one comment under an article in the left-wing newspaper Público, by a reader named as Bender.
"There are few such absurd ways to lose your life," said another, called Vivaercante.
The animal rights political party, PACMA, meanwhile, began a campaign to save the mother of Lorenzo, the bull which killed Barrio, and which is due to be slaughtered, as is the custom when a matador is fatally gored. "Bullfighting is thirst for blood," the party tweeted.
Supporters of bullfighting supporters have hit back. "It doesn't make you any more of an animal lover just because you're happy at the death of a human," said Frank Cuesta, a elevision presenter.
For centuries, the sport has been seen as part of the fabric of Spanish life, but opposition to bullfighting has been gaining ground in recent years, with opinion on the issue dividing along party political lines.
Earlier this year, Podemos, the left-wing anti-austerity party, proposed a ban on bullfighting in the Balearic Islands, and the southern city of Cordoba stopped funding its annual fiestas. The Socialist mayor of Valencia, a major bullfighting city, sparked uproar by suggesting that bulls should no longer be killed during Spanish bullfights, as is the tradition in Portugal.
In 2012, Catalan nationalists outlawed bullfighting in their region. A poll taken by Ipsos MORI in December 2015 showed that only 19 per cent of Spaniards aged between 16 and 65 were in favour of bullfighting, down from 30 per cent just three years earlier.
Ms Sanz, the widow, is a local politician in the town of Sepulveda for the conservative Popular Party (PP), which staunchly supports bullfighting.
In an emotional message last night, she said that life was "unfair" and posted a poem by the Spanish writer, Jose Leon, which ended with the words: "How I would love to believe that there is glory for all those who lose their lives on the horns of bulls."