Why does it bother us when someone gets something they didn't work for?

Why is it that when I'm talking about my liberal ideas, I always get someone who thinks that giving a baseline payment to everyone, or making food non-profit, or making any number of other ideas that might help the poor out of their rut means that someone is going to abuse the system and get something they don't deserve? What does it mean to deserve something?

Does a poor, single mother of one kid deserve to have food to feed her kid?

Does a poor, single mother of eight kids deserve to have food to feed her kids?

Does being poor and having many kids somehow make getting the food to feed the kids an abuse of the system? Is it an abuse of the system if, because of economies of scale, you can afford to trade some of that food for cash?

Is shutting down systems that can be abused to avoid the few scammers worth hurting the truly needy majority in the program?

Will it be moral to charge for food when machines grow and harvest enough food for every person on the planet without human input?

When something is post scarce, what good does it do to charge money for it, other than ensure that there are people who don't get access to it? Is it moral to do so?