Basically, what Peter Lumetta said. But a lot of parents were concerned because their music was so based at teens, their lyrics were somewhat disturbing. Listening to songs about dating underraged girls like in Christine Sixteen made a lot of people worry, especially as the band got older.
However, it was a lot better than AC/DC's sexism on tape, and parody metal band GWAR was highly inspired by KISS. If not for the makeup, the style of music and general songwriting, bands such as Judas Priest, Motorhead or Iron Maiden wouldn't be as successful today. And without them, Metal wouldn't be as highly devolved as it is today.