No PR firm would have dreamt up the word "brutalism". The term was derived from Le Corbusier's "Breton brut"- French for "raw concrete", the movement's preferred material - rather than anything to do with brutality, with which it has sadly become better associated. In the popular imagination, brutalism is synonymous with harsh, hostile, ugly architecture (or death metal). Two key examples of the movement are currently under threat, Birmingham Central Library and Robin Hood Gardens, and both have sparked furious debate.

Birmingham Central Library, opened in 1974 and designed by John Madin, is apparently the busiest library in Europe, though Prince Charles judged its hulking inverted ziggurat more suited to incinerating books than storing them. The building was slated for demolition as part of a £1bn plan to regenerate the city centre (and build a brand new library) but now English Heritage has recommended it be listed, arguing that it has "defined an era of Birmingham's history". There seem to be plenty in the city who would rather leave that era undefined, but others have defended it as a successful, high-quality design, including my colleague Jonathan Glancey.

It's a similar story with Robin Hood Gardens, in Poplar, East London. One of the original "streets in the sky" housing developments, completed in 1972, this relentless mid-rise estate displayed the worst of public housing design: crime, grime, and societal and material decay. But it was designed by Alison and Peter Smithson, arguably Britain's most celebrated modernist architects. When discussions over its future arose, the architectural magazine Building Design launched a campaign to save it led by heavyweights such as Richard Rogers and Zaha Hadid. As Simon Jenkins pointed out, nobody who actually lives there has joined this campaign. Why not please everybody and convert it into a National Museum of Bad Architecture?

Simon Jenkins' condemnation of Robin Hood Gardens, "a twin-slab estate of flats in east London ... grimly sandwiched between a main road and the approach to the Blackwall tunnel", may entertain but contributes little to the debate about the re-use of historic buildings (This icon of 60s New Brutalism has its champions. So let them restore it, June 20).

The late Peter and Alison Smithson, far from being uncritical "followers of Le Corbusier", were among the first architects to criticise the inhumane consequences of his theories. Against prevailing modernist orthodoxy they thought there was much to learn from traditional streets and the fine details of the way peoples occupied and personalised space: "The short narrow street of the slum succeeds where spacious redevelopment frequently fails."

Robin Hood Gardens was to be an essay in applying such lessons to the compact high-density housing surrounded by shared green space that was then widely thought to be the future. Let us laugh along with Jenkins at some of the Smithsons' "architectural gobbledygook", but when they spoke of a "quietness that until now our sensibilities could not recognise as architecture at all" they were radically championing the subtle and timeless qualities found in undemonstrative everyday places.