I don't think I've ever seen anyone advocating the inclusion of people with fatal heart defects on space missions just to satisfy a goal of improved diversity.

There are a lot of people out there who want to become astronauts and are rejected because they're not healthy enough. The reaction is almost always "that sucks for you, maybe you could go into something related to space so you're at least still doing something related to your dream," not "NASA sucks, they're building weaker teams by excluding people they think aren't healthy enough for space travel."