Answer by taking a quote from the following article:

John Bruce "Jack" Thompson (born July 25, 1951) is an American activist and disbarred attorney, based in Coral Gables, Florida. Thompson is known for his role as an anti-video-game activist, particularly against violence and sex in video games. During his time as an attorney, Thompson focused his legal efforts against what he perceives as obscenity in modern culture. This included rap music, broadcasts by shock jock Howard Stern, the content of computer and video games and their alleged effects on children.

In 2004, Thompson helped get Howard Stern's show taken off a radio station in Orlando, Florida by filing a complaint with the Federal Communications Commission. Thompson objected to Stern's use of perceived obscenities on the air. He argued that "Either broadcasters will accept the light harness of decency that has been the law for decades and start cleaning up their acts, or the public's deepening outrage will foster a more fearsome governmental response." Thompson claimed to have received death threats from listeners of Stern's show, noting that "you'd expect that considering the IQ of people who listen to Howard Stern. Apparently they fail to realize that I might have caller ID."  During his opposition to Howard Stern, Thompson was asked in an interview with a reporter if, by his standards, he would blame Christianity for the murders committed by Michael Hernandez, a fourteen-year-old who murdered one of his classmates in 2004, because Hernandez wrote a diary in which he constantly spoke about praying to God. Thompson replied, "The Bible doesn't promote killing innocent people, Grand Theft Auto does. Islam does." Thompson then expanded his comments in the same interview by saying, "Islam promotes the killing of innocent people. The Quran requires the infidel, whether Jew or Christian, to be killed. ... That's a core essence of the religion. ... Muhammad was a pirate who killed infidels and who advocated the killing of infidels--not a nice guy. Osama bin Laden is in keeping with his fine tradition."  He later spoke in defense of Stern during the latter's legal dispute with CBS over promoting Sirius on-air before his switch to satellite radio. Thompson contended that the technology added by CBS to edit out profanity also could have worked to edit out Stern's references to Sirius. According to Thompson, "The reason why CBS chose not to edit Stern is that Stern's Arbitron ratings remained high and were arguably even enhanced by people tuning in to hear daily about Stern's running feud with CBS and his move to Sirius. In other words, CBS actually used Stern's discussion of his move to Sirius to make more money for CBS."  CBS President Leslie Moonves responded, saying "You know what? You can't let people like that tell you what to put on the air or what not to put on the air. That would only open the door when suddenly next week, he says, 'Take David Letterman off the air or take C.S.I. off the air.' Or you know what? Everybody Loves Raymond was about, you know, sex last week or about a 70-year-old man--you know, we dealt with Peter Boyle having sex with Doris Roberts. 'Take that off the air.' That's something we can't let happen."

Why was he on The Howard Stern Show?
Thompson helped get Howard Stern's show taken off a radio station in Orlando, Florida by filing a complaint with the Federal Communications Commission.