"Negative eugenics" aims to cut out traits that lead to suffering, by limiting people with the traits from reproducing. "Positive eugenics" aims to produce more healthy and intelligent humans, by persuading people with those traits to have more children. In the past, many ways were proposed for doing this, and even today eugenics means different things to different people. The idea of eugenics is controversial, because in the past it was sometimes used to justify discrimination and injustice against people who were thought to be genetically unhealthy or inferior.