I'm generally pretty biased against all religion by default but Sikhism is one of the few religions I can't find much to complain about. It's pretty egalitarian, its followers are encouraged to defend the weak (and not just weak Sikhs either) and committing to its values and laws is an option that should only be taken after careful consideration rather than the default. The only negative thing I can think of is the insurgency in India of the 1970s and the assassination of Indira Gandhi, although I don't think it's fair to classify those events purely as religiously motivated violence (or even terrorism).
It's not great to pick and choose whether to stereotype people based on religion, positively or ngatively. You may have forgotten the blowing up of a 747 carrying 329 people, suspected to have been by Canadian Sikh militants https://en.wikipedia.org/wiki/Air_India_Flight_182
In the aftermath of 9/11, there were many snarky remarks in the Blogosphere about "those war-like Buddhists", implying that Buddhism was entirely peaceful, when Buddhism is in fact co-opted in various ugly political ways in South East Asia.
Religions are not abstract ideologies, but always exist in the context of their practitioners.