This is true; but such pleas, made under duress, are overturned. Threatening to attack your family, for instance, is not the same as saying, "do you want to roll the dice with a jury and risk the death penalty? or do you want to cop a plea, keep your options open for appeals etc."
But it can lead to people pleading guilty to crimes they didn't commit. General Mike Flynn for example.
This is true; but such pleas, made under duress, are overturned. Threatening to attack your family, for instance, is not the same as saying, "do you want to roll the dice with a jury and risk the death penalty? or do you want to cop a plea, keep your options open for appeals etc."