Nowadays though, they manage together ( HDB, TC, CWS and the people themselves with usually the CWS as mediator ) to find a peaceful resolution and people can most of the time keep their cats.
Quite a few people have cats in HDBS, and HDB and the respective TCs are well aware that many people do have cats and they choose not to actively enforce the no cats rules as long as nobody complains.
edited to add: and you don't need to live in HDB to have neighbours ticked off and calling AVA to euthanise your cat... it's a danger anywhere in Singapore, as soon as your cat gets out wether or not you can legally keep it in your home. I've seen it happen in private housing too.