Josh Horwitz, the executive director of the Educational Fund to Stop Gun Violence, which monitors firearm-related homicides and suicides, said that “extreme gun culture” had become pervasive. “Only in America can a 17-year-old grab an assault weapon, travel across state lines, provoke a fight, kill two people and injure another and pay no consequences,” he said after the verdict on Friday in Kenosha, Wis.

Some Black Americans viewed the verdict as more evidence of racial disparity in judicial outcomes, a perspective that extended to the discussion around the right to bear arms.

The Rev. Al Sharpton contrasted the acquittal of Mr. Rittenhouse with the federal government’s aggressive, at times violent, campaign against the Black Panthers and other Black groups that cited self-defense and the Second Amendment as justifications for arming themselves.

“There’s a huge double standard,” he said in an interview, arguing that a Black man who did what Mr. Rittenhouse did “would have been convicted in two hours.”

The National Rifle Association, which has backed “stand your ground” laws to expand the legal defense for gun owners who shoot people they perceive to be threatening, responded to the verdict by posting portions of the Second Amendment on its Twitter page. “A well regulated militia shall not be infringed” it wrote, minutes after the jury delivered not-guilty verdicts on five counts facing Mr. Rittenhouse, including first-degree intentional homicide.

Other advocates of gun rights were still more outspoken. Representative Madison Cawthorn, a North Carolina Republican, urged supporters to become “armed” and “dangerous.”

The Gun Owners of America, which has staked out a position to the right of the N.R.A. in hopes of capitalizing on the larger group’s recent leadership and financial woes, on Friday announced its intention to send Mr. Rittenhouse, now 18, a new AR-15 rifle in reward for his “defense” of the Second Amendment.