The debate, the first between opposition hopefuls since 2011, was held as they await a ruling by the country's top court which could suspend the Oct. 22 nominating contest.
Independent candidate for 2024 Luis Ratti - who many in the opposition say has ties to the ruling socialist party - asked the Supreme Justice Tribunal on Monday to bar the primary on unspecified allegations of irregularities.
Venezuela's often divided opposition is seeking to dislodge President Nicolas Maduro, who has ruled the country since 2013.
Though the last election in 2018 was widely condemned, especially by the United States, as fraudulent, the opposition has so far failed to unseat Maduro.
Three of the most high-profile of the 14 opposition hopefuls, Maria Corina Machado, Henrique Capriles and Freddy Superlano, have already been barred from holding public office.
The primary must give the opposition clear leadership and stronger unity, said the eight candidates who attended the debate, organized by non-governmental groups and hosted at Universidad Catolica Andres Bello.
"We need a leadership that does not hesitate, that confronts, that is incapable of bending in the face of threats," said Machado, a 55-year-old former lawmaker who is leading polling for the primary.
"This is not a conventional election," said Superlano, who warned any of the candidates could be banned. "We need leadership who will take the fight to the end."
However, there was disagreement about how to choose a replacement if the favored candidate was barred from running.
Two-time presidential candidate Capriles was notably absent. He said on Monday the country needs the opposition to be unified, not airing its differences in public.
The hopefuls said private investors must feel confident returning to Venezuela, whose economy contracted for eight consecutive years until 2022, when it showed incipient growth which is already waning.
"We propose ... reinserting the country into the global financial system to attract investment. Productive expansion means openings markets, privatizing, and respecting private property," Machado said.
Superlano and other hopefuls, including former lawmakers Delsa Solorzano and Carlos Prosperi, said laws were needed to ensure respect for private property, increase employment, and revise rules which allow the state a majority participation in oil companies.
"We need to move from extractive development to productive development, to a free-market economy that obliges the inclusion of those who have been left behind," said former legislator Tamara Adrian.
(Reporting by Vivian Sequera, Mayela Armas and Deisy Buitrago; Writing by Julia Symmes Cobb; Editing by Rosalba O'Brien)
