He said the decision was the "utterly stupid result" of what he termed ill-conceived earthquake legislation brought about by "knee-jerk policy of an insanely risk-averse society and government".
"During the past 100 years we have lost fewer than 450 lives to earthquakes. That's, on average, 4.5 lives per annum. Our reaction has been to demolish, replace or rebuild all buildings that are at risk, no matter how useful, no matter what the expense," he said.
"Do we ban all motor vehicles and roads until we can reduce the risk of death by that cause also to 4.5 lives per annum? No, of course we don't. That's stupid. That's illogical.
"All I'd ask for is some rationality in the discussion."
He said the family received a letter on Friday about the meeting on Monday "so we were forewarned" but were not aware they were going to be told the home was closing.
"Mum's fine because she's always been phlegmatic," he said.
Now her family were looking for another home for her.
"We've got her name down at Kowhainui although they don't have any beds free there at the moment."
But Mr Dowdeswell said it was a knee-jerk decision to close the home.
"What would be wrong with letting the Home of Compassion demolish what it has to sensibly and replace it, sensibly, over time?
"They've looked into what needed to be done and how to do that and we were told it would take a couple of years at least, either strengthening it or rebuilding it altogether."
But he said the process seemed to be totally irrational.
"Why not tell everyone they can't live in Wellington because they might get a really big quake?"
He said he fully supported the Sisters of Compassion but believed they were "between a rock and a hard place".
"They can't do anything else the way the legislation is," Mr Dowdeswell said.
He said the nation was wasting hundreds of millions of dollars of huge, perfectly usable and valuable resources.
"The majority of the unsafe buildings will undoubtedly be replaced for economic reasons over the next 50 years anyway. This is an insane, tragic waste of public resource and all for the sake of emotion.
"My mother is perfectly happy to stay there. I would be perfectly happy to stay there when my time comes too," Mr Dowdeswell said.
Sister Margaret Anne Mills, leader of the Sisters of Compassion, said they had not sought costings for restoration or full replacement of the complex.
"Doing either would have meant relocating residents and staff and we have experience before of doing that and know how stressful and difficult it can be," Sister Margaret Anne told the Chronicle.
She said the home was refurbished in 1999 and that meant shifting the entire operation from its Virginia Rd site to the then recently-vacated Jubilee Hospital in Aramoho.
"That was a huge upheaval at the time and something we just couldn't do again."
She said they also looked for a similar temporary location in the city if they opted for a rebuild but there was nothing suitable.
"It was on that basis that we decided, very reluctantly, the service would have to close.
"We've been going round and round in circles trying to resolve our problem but had to make the hard decision," she said.
Sister Margaret Anne said it was still too early to talk about the future of the site but said the sisters were determined that whatever the outcome, their legacy would stay in Wanganui.