Haven't some major terrorist attacks actually been the work of Sikhs?
Seizing of the Golden Temple in Amiritsar was the work of a Sikh group and I think there was a bombing of an Air India plane in the late '80s.
Yes - actually, the second-deadliest terror attack of all time (the bombing of an Air India 747) was the work of Sikh extremists.
However, I'm unaware of any Sikh extremist terror attacks for quite a long time - it was largely from a movment for independence for the Punjab (Khalistan) from India, around the period militants took control of the Golden Temple at Amritsar and the Indian Army shot up the place badly in taking it back, follwed by the President of India (Indira Gandhi) being assasinated by her Sikh bodyguards.