How stupid is too stupid to reproduce?

Is there a certain level of stupidity at which people wouldn’t reproduce? I met a lot of pioneers in researching this today. I had to go to Walmart and it was a really great day out. And the woodchucks were out in droves. Obese father, obese mother, and obese kids, all completely blocking the aisles. And they wouldn’t move. I had to ask them to let me through. It was so annoying. I just wanted to put my head down and charge them with the cart, but I’d just bounce off. Or they stand in the middle of the aisle yakking on their cell phones. I hate inconsiderate people.