Teaching unions also claim an opportunity to reduce class sizes has been missed.
But the city council insists the "unprecedented" proposals - affecting dozens of schools - are the best way to save pound;3m a year currently wasted on empty desks, and fund improvements to other schools.
It has also refused to promise to avoid compulsory redundancies. Officials believe actual redundancies will be minimal, however, as a result of natural wastage and redeployment of staff to other schools over the next 10-15 years.
As in other parts of Wales, parents, pupils and teachers in Cardiff have reacted angrily to closure plans, affecting six high schools and around a dozen primaries. Other schools will be merged or admit fewer pupils.
But there will be a third Welsh-medium high school, and five more primaries.
Surplus places are a problem in every local authority in Wales. In 2004, there were nearly 73,000 empty desks, and declining birth rates mean there will be a further 40,000 fewer pupils by 2013-14.
Some local authorities, such as Carmarthenshire, have already started closures and mergers - but have also used reorganisation as an opportunity to improve remaining schools.
A TES Cymru survey last year suggested the backlog of school repairs stood at more than pound;785m. Many primaries still lack basics such as a school hall and staffroom, and even indoor toilets.
Cardiff city council says its proposals should get rid of all temporary classrooms, eradicate its pound;60m repairs backlog, and ensure all schools are fully accessible to disabled people.
Dr Philip Dixon, director of the Association of Teachers and Lecturers Cymru, said: "A number of our members are in schools earmarked for closure.
ATL will obviously be fighting for the best deal for them, and pressing the council to give us a categorical assurance that there will be no compulsory redundancies.
"But we will also be looking closely at the principles behind these proposals. Some of them are eminently sensible - especially those that would lead to more socially balanced intakes. The plans should be judged not by the money they save but by the ways in which they will improve the education of all Cardiff's children."
The National Union of Teachers Cymru has claimed that more than 300 teachers' jobs could be lost, and heads have previously speculated that up to 700 teaching and non-teaching jobs could go.
But Hugh Knight, Cardiff's chief schools officer, said: "We believe this can be managed, particularly if governing bodies co-operate fully with our new redeployment policy.
"We would ask governors (with vacancies to fill) to always consider staff affected by reorganisation first, rather than recruiting from outside the city."
Consultations, if agreed by the full council, will close on July 21. See www.cardiff.gov.uk