I wouldn't confuse a hyperbolic post about how someone who sets fire to a 3 year old should be "taken out and shot" for the poster's actual opinion regarding the justice system or due process.
Also, I think a lot of the rhetoric simply omits "if convicted" because it's implied. Frankly it's a testament to the faith in general of out judicial system that we're so readilly willing to allow the govt to pass judgment on criminals. In Iran, for example, you have state run media telling you a certain protestor or dissident was also a child murderer and that's why he was killed. If you lived in a country where persons you knew to be innocent were being tortured or killed by the govt I doubt you'd see much enthusiasm for the police or justice system carrying out their duties.
To the extent someone says "No trial, just kill them" and really means it, that person is dumb.