This is a difference I am trying to teach my daughter. It makes me unpopular sometimes when people think I need to make her "share". If I make her do it, it is not sharing.
I don't want her to grow up as one of those idiots (such as the president, congress, and other various puppeticians and bureaucraps) who think it is nice to give welfare to poor people. Charity, with your own money- great. "Giving" money that was never yours to give, which you supported being stolen under threat of death- not such a "good thing".
I do encourage my daughter to share, and ask her to put herself in the place of the other kid. But if she chooses not to share I will not force her to hand over her toy.
And, I never let her get away with forcing other kids to share with her, either. If the other kid's parent tries to force their kid to share I ask that they not do so.
Voluntaryism makes all the difference.