I read a good book about the fiasco that was the Air India tragedy where Sikh extremists took down a flight killing hundreds of Canadians.
From the accounts it was actually Sikhs who tried to get the RCMP interested in what was going up months before the event, but the RCMP dropped the ball.
So while there are or were extremists in their midst, generally as a community they are not anything like Muslims.
Indira Gandhi was assassinated by her Sikh bodyguards.