Yes yes I tend to agree that the we should not exaggerate gravity of covid-19. But this question of app is not only covid-19 but also any possible future epidemic. Imagine tomorrow we face a similar virus but it kills 50% of people infected, or worse 90%, would you really say we should not use such an app, even though it is harmless for privacy?
Also it is always quite easy to say this kind of things about natural selection, when ourselves face a low probability of death (because we're young, that's my case, I guess it's yours), and others face a way higher probability. We might not say the same thing if we were facing death directly. And also it's not only a question of dying, but also dying in terrible conditions, if heath systems are overwhelmed. We have been habited not to face this anymore, these last decades.
And also do not forget that this app would not only save lives or give us security, but help us get back our freedoms, freedom to go out, and to meet people, while we are already confined.