It seems to me that people who believe government should redistribute wealth do not believe that someone with the opportunity to make more money should have to do so, in order to use their money to help others, only that once they have made the money, they must give some to others.
One possible explanation is that they see our obligations to one another as limited- of course you don’t have to take that promotion for the good of society, but if you take it for your own good, society had better get some of the action.
Yet redistribution is usually justified on the grounds that two people with the same intentions, the same willingness to sacrifice, but different opportunities, can end up with different incomes- it is the opportunity, not the willingness to sacrifice, that you are paying for. Yet the debt kicks in only on someone who is willing to make the sacrifice. Again, we’re talking here only about the situation where someone has an opportunity to earn more money, but for whatever reason prefers a lower-paying job.
For a previous post of mine on redistribution, see here.