Christianity only appears less "radical" than Islam because the west has secularized
The inherently radical nature of what ALL the Abrahamic religions are if the texts were followed word for word instead of the "picking and choosing" you often see in modern times has been tamed in the west by the legal and government systems themselves becoming largely secular. Those radical christians you speak of are more rare and even if they are extremists they are less likely to act on it because it is not socially acceptable, which has nothing to do with Christianity itself being less inherently extreme or violent than Islam. The reason Islam seems more radical is because the government itself is radically Islamic in many muslim countries. If there was a christian fundamentalist government it would be just as extreme and oppressive but as it stands most countries where christians are the majority have more modern secular standards of morality and legality than the "stone gays and burn scientists at the stake" mentality that you saw when the church was in power.