> Who tells your phone that you’ve been diagnosed, for example? Given the possibility that – in a post-lockdown scenario – individuals with Covid-19 might be subjected to stigma, harassment or dismissal, they might be understandably reluctant to broadcast the fact. Then there’s the problem that not everyone has a smartphone, even though it’s commonly supposed in tech circles that they do. The pandemic has revealed that a significant minority of the population (mostly older people) still relies on olde-worlde feature phones. Moreover, it turns out that not all smartphones are created equal: one estimate is that 50% of all smartphones can’t use the proximity-sensing systems being developed by Apple and Google.
...which is followed by a hand-wavey "I could go on but you get the point".
All three complaints are about how effective the solution might be, not actual reasons why it would "kill democracy".