Having a first degree relative - parent or sibling - with anxiety and/or depression about doubles the risk of developing a disorder. The lifetime prevalence of these disorders is ~30%, and for all psychiatric disorders about 40-45% so if your advice were followed there would soon be a large population crash, which would delight the environment, but I doubt you'd persuade many to take your advice to heart.
The other factor is not all the genetic risk comes from DNA, epigenetics may be as big a factor and there is no way of predicting who is vulnerable.