It wasn’t always the case, but nowadays I believe that our urge to freely share, reflected (also) in the existence of free licenses (and consequently in dual licenses as well), is misguided.
I believe that giving stuff away for free is an aberration; it is a throwback behavior that evolved in times when “free” sharing was accompanied by a different behavior, one that made everybody to share equally. Anthropologists claim that our hunter-gatherer ancestors lived in egalitarian groups where all resources were shared equally. The system was supposedly maintained by “intentional leveling” - a process the group members imposed on individuals who defected from the rule. The original leveling behavior works in small groups, but is unenforceable when the group member numbers exceed something like the Dumbar number. Apparently, in the last 15 to 30 000 years, humans started living in large aggregations and the original leveling mechanism lost its power. Now we are stuck with half of something that used to be beneficial for us. The behavior now works against our individual and collective economic interests.
I believe we must develop a modern version of the leveling mechanism, that will force everybody to reciprocate. We need to reject any forms of free sharing, if such sharing is not done by everybody.
I believe this should be reflected also in the licenses governing use of open source software.