Florida Congressman Bill Posey grilled Facebook CEO Mark Zuckerburg at a recent House Financial Services hearing.

Posey stated, “I support vaccinations of children and adults, but I also support open and frank communication about the risks of vaccination,” Posey told Zuckerberg. “You testified that you believe in giving people a voice. Is Facebook able to assure us it will support users’ fair and open discussions and communications about the risks as well as the benefits of vaccinations?”

Zuckerberg said anti-vaccination users on Facebook have the same rights to expression as others, and their views aren’t censored. However, he said, they aren’t publicized, either.

“If someone wants to post anti-vaccination content or they want to join a group where people are discussing that, we don’t stop them from doing that,” said Zuckerberg. “But […] we don’t go out of our way to make sure our group recommendation systems show people or encourage people to join those groups. We discourage that.”