That 21% figure is about the same as the percentage who call themselves "liberal" in opinion polls. 20% of the country are nuts.
Eighteen years ago, when I first began commenting on this subject in Free Republic, my estimate was 15%. Clinically nuts, including all voters.
Astonishingly, today, my personal estimate is between 50% and 70%, based on their ignorance, irrational violent behavior, and total unawareness that they are self-destructing.
Survival dictates that Society will react with superior violence, no mercy, and utter finality.*
If their number keeps increasing, who knows what form the final social suicide will take?
* The Kent State Shootings, 1970, absolutely brought irrational, violent, felonious "protests" to an immediate and long lasting halt.
Please spare me the asinine, "we are better than China or Russia or whatever. The number of innocent, normal, rational bystanders who die is paramount. The insane are not.