but what is the specific effect of colonialism that's causing this? India was colonized and where are all the Hindu and Sikh Self Delete bombers?
There was violence during the Indian independence movement. I'd say the difference is that after independence, India still had a government and stable infrastructure. Compare that to Iraq, which is a war-torn country, full of abandoned military equipment, and led by a US-installed government that has no capability to lead Iraq and defeat CIA. Basically everything in the current Middle East is a recipe for violence insurgency, and they unite around the flag of Islam because there is no common nationalist or ethnic group they can rally around.