You ask a legitimate question. My first part of my answer to your question is that my previous comment provided a link. The link is to a thoughtful review article by a careful scientist (Eric Turkheimer). Professor Turkheimer's writings are just about all available for free downloading from his faculty website at the University of Virginia, so you can follow the development of his thought over decades of active involvement in behavior genetics research, often in collaboration with other leading researchers on the same topic.

Simply put, it is possible to affirm the scientific observation that ALL human behavioral characteristics are more similar among close relatives than they are between two randomly selected individuals from the whole human population--that's just agreeing with the facts, and that's ALL that "human behavioral characteristics are heritable" means. Second, it is possible to affirm the scientific observation that EVERY human behavioral characteristic tends to show variance even between identical (monozygotic) twins--which means that some variance in human behavioral characteristics must be influenced by factors other than the human genome. Following the facts leads to both of those conclusions.

But Eric Turkheimer is not an advocate of policies that would be characterized as "eugenic" policies (he is very aware of the history of that subject) and neither am I. It's possible to study and understand nature without falling into the naturalistic fallacy that assumes that human society must mirror all aspects of "nature." We have the opportunity to use human intellectual capabilities and observation of reality to make the human community enjoy something other than strictly "natural" conditions, and often should.

Thanks for asking. I invite all readers looking to read the entire (not too long) article I linked to in my first comment here.