If you had family history of an untreatable disease that you had 50% probability of inheriting but it typically sets on later at like 40 years old

I would want to know. And even results are usually just probabilities. Plus 20 years of anxiety about it and besides you can keep up on it and with some conditions what you do in your 20s like diet can make symptoms less severe down the road like type 2 diabetes or circulatory related conditions.