Johnny is a Whig, so on one hand, it would make sense for him to support the Whigs in beating up the Tory. However, the violence (the threat he's hearing outside, and the threat of violence later, depending on what happens with the tea ships) clearly disturbs Johnny. This is something the novel links to Johnny’s youth and innocence. Rab, on the other hand, is several years older and way more mature, so he understands better that this violence has a purpose. And Mr. Adams—clearly an adult—understands best of all that a war might be coming, and with it, violence.