He said he will bring up the possibility of council leading legal action against the church at the next meeting.
"I don't know if all councillors would have the guts to do that, because that would be a very strange situation, where you have the council taking on the church," he said.
"What I'm also going to call for ... is a televised debate, a full one-hour televised debate, with all the facts being laid on the table from both sides. We need to hear from (engineer) Kit Miyamoto and his plans and those of other engineers, and the People's Steeple on one side, and we need the engineers that have been contracted by the church on the other.
"If the public decide they'd rather have a sandpit in the middle of the square, then that's fine if that's what the public want. But I believe there is a lot of public that actually want to hang on to a bit of history.
"In context to the $39 billion rebuild of the city to keep your symbol of the city ... it's small."
Engineer Michael King from Cardno is also calling for the debate.
"You could get 100 engineering experts from around the world that will tell you that building can be saved, I've had offers from many of them who want to come here and help" he said.
Mr Keown backed the People's Steeple model, where the bulk of the cathedral is preserved, and a wooden steeple is constructed to replace the cathedral's collapsed stone bell tower.
He was confident the $20 million needed for Mr Miyamoto's plans, which involve earthquake strengthening, base isolation and repair work, could be raised by the end of the year.
"We have to get a fund going, but the church has to be prepared to negotiate, otherwise people aren't going to part with that money.
"I know the money will roll in."
Mr Keown has bought the website name savethecathedral.co.nz, which he hopes to be live by the end of the week, and has plans for t-shirts and calendars to raise funds.
Mr Keown, an Anglican himself, said there was still a "reasonable chance" the demolition decision would be reversed.
"I'm quite optimistic, because I've got faith, I am an Anglican by faith ... and I believe they will listen if there is a big enough groundswell.
"This is the largest debate of the earthquake. Forget Tony Marryatt's salary, forget the city plan, forget the insurance, this is the biggest debate.
"The church ... have overlooked the passion of the people of Christchurch for that building. The Wizard, who is an atheist, is wanting to save that building above all others.
It's beyond just a cathedral - there is so much ownership by the people of Christchurch, that cannot be underestimated.
Mr Keown said if the "symbol of our city" is lost, "the earthquakes have beaten us".
"You might as well not build the city in the middle of the city. You might as well just move west to firmer ground like some people around the country want.
"That church anchors us to the centre of the city, to our history, and to what we've planned."