Faith based reasoning is by no means more common with the religious right, that's just your bias speaking. 
If you interpret the term "faith" to mean non-logical reasoning based on fixed  assumptions and not just organized religion, the left and right are about equally guilty. Consider any number of half-baked social movements, or for that matter "scientific socialism" itself (as described by Marx, no less) and you will find just as much faith as in any church. The fact that many people continue to support socialism despite the events of the past 100 years demonstrated that reactionaries share the same intellectual swamp as many on the left. It's a near-universal conceit of the left to believe otherwise, but it's still just conceit.