See my long response elsewhere. Depending on incidence rates and whether or not the effect of following up earlier is sufficiently large, there can - and sometimes is - a net detrimental effect to wrongfully diagnosing someone with a condition. Even when following up is relatively simple and risk free, and lives are saved by finding conditions early.

E.g. cause an extra million doctors visits due to wrongly diagnosing people, and the incident rate of e.g. extra infections transmitted from another patient, or compounded misdiagnosis leading to extra interventions which have some risk of failure, or even just accidents on the way to the doctors office, very quickly leads to extra harm just from the sheer volume.

That extra harm might be worth it, if the early diagnosis of others save enough lives - the same way seat belts kills some people but save far more. But it also might not, e.g. if the condition is rare enough, or early detection have little enough effect in improving outcomes.