Kelley defended the show's liberal leanings during Monday panel discussion at the Museum of Radio & Television, TVWeek.com reported.
"We seem to be living in a time when dissent is very much equated with disloyalty," Kelley said. "(Our) writers want to scream sometimes, and inspire some of the viewers to scream along with us."
Among the issues "Boston Legal" has tackled from a liberal perspective were the morning-after pill and assisted suicide.
Admitting he was "sort of stunned" the show is headed into its third year, Kelley joked, "We believe there's something in every show for everybody -- to turn off."
Star William Shatner said the Nielsen ratings do not do "Boston Public" justice.
"The Nielsen numbers lie," the former Capt. James T. Kirk said. "We are far more popular than our Nielsen ratings. It's the most popular thing I've ever done, including 'Star Trek.'"