He went on to criticise Prime Minister Jacinda Ardern for the Christchurch call summit in Paris, which resulted in major tech companies committing to better detect and remove extremist content.
Prebble told attendees his father waded ashore during the Normandy landings for freedom, and not so Ardern could "limit free speech" and "perform on CNN".
Seymour darkly warned of the liberal left working in the background of the Government to "censor citizens' thoughts and speech".
His response will come on Tuesday, when he submits a member's bill to repeal parts of the law that makes speech unlawful if it is abusive or insulting and likely to "excite hostility" against a group of people, or bring them into contempt on the ground of their colour, race or ethnicity.
Protecting free speech and opposition to rushed gun reforms fits with Act's ideological opposition to government interference in individuals' lives.
However, it's led to accusations that, in the wake of a terror attack targeting Muslims, Seymour is dog-whistling to racists.
He strongly denies that. Supporting free speech means standing up for statements you don't believe in, he says, and it's deeply unfortunate that some people "try to conflate me with the people I'm standing with".
But won't some racist voters make the same conflation?
"I think there are probably one or two people like that," Seymour told the Herald after his speech. "But you've got to be careful that you don't say the overwhelming majority of people who think free speech is important are racists."
Whatever the mix, they and unhappy gun owners are being targeted to help Act lift its 0.5 per cent of the vote.
During the conference Act members were told the event was one of the most important in the party's history, and a relaunched Act could get at least 14 MPs elected next year and install Seymour as Deputy Prime Minister.
Asked afterwards if that was delusional, Seymour paused. "Well, possibly. Because I think Act would always sit on the cross-benches."
