It makes people happy to use defensive force

Without property rights extending to things like land, we cannot live peacefully and abundantly. If we cannot retain (the product of) our labour then we will have no incentive to create it, and there will be no complexity. We have a right to deny to others what we have made ourselves, if it (ownership) is not idiosyncratic to the person who made it then there are no proper incentives. Our individual actions are immoral if we contravene that which is pragmatic. We are immoral if we reduce happiness.

The use of force in defence of property rights is then acceptable because this provides the environment which allows the most happiness. If goods are combined and we have no choice but to share, then there is little incentive to produce (we can still take the same amount) and without the incentive to produce there will be no production and people will starve. Collectivism removes the incentive to work. There is no reason to force people to share their produce. Collectivism is not pragmatic; it is pragmatic and moral to leave people alone.