First, not all Americans were slave owners. Slave were expensive and only the rich could afford them.
Second, you need to compare the tactics used by the American colonists to those of the Iraqi insurgents.
Warfare during the time of the American Revolution consisted of the two sides lining up in ranks across a field and firing volleys at each other then charging with bayonets. The unconventional tactics used by the American militias consisted of hit and run attacks, snipers, fighting from within forests and cover and ambushes of military forces. Basically, what is considered conventional fighting today.
The Iraqi insurgents are killing indiscriminately. They don't care if they kill civilians and often target civilians. They use terror tactics, such as torture and beheadings of civilians. They use bombs against both civilian and military targets. They strap bombs on to children.
You mention the militias of the American Revolution (MAR) and the Iraqi militias (IM).
The MAR were citizen solders raised by the individual colonies because they colonies did not have armies. They rose up to fight a common enemy who was oppressing them.
The IM are citizens who have armed themselves to support a person or group vaying for power. The are fighting more among themselves than they are resisting the U.S. The U.S. is not trying to oppress the Iraqi people. The IM groups are oppressing the people they consider different or undesirable. This can be seen in the Sunni and Shiite militias forcing people of other sects out of neighborhoods to make single sect only neighborhoods. They are forcing people out by threat of violence and murder. This would be the equivilent of the KKK forcing black and hispanic people out of mixed neighborhoods to make white only neighborhoods and the Black Pathers or Nation of Islam forcing white and hispanic people out of black neighborhoods to make black-only neighborhoods.