Company refuses to give a temp employee a raise, despite promoting him to a role that requires the workload of a full-time employee: 'I'm making minimum wage.'

If he is doing more work, he should at least have the benefits of being a full-time employee instead of a temp.

You should feel lucky if you've never had to do temp work. Those jobs are not for the faint of heart. You never feel like you're quite secure in your position, and that's because you're not. You can get fired anytime for literally any reason. You don't have the same protections and benefits as full-time employees. 

There are some benefits to working a temp job that you won't get anywhere else. You can quit whenever you want without having to worry about the bridges you've burnt. Everyone in a temp agency knows that you don't sign up for these jobs with the intention of staying there for your entire career. They're called temp jobs because they're temporary! Depending on your temp job, it might also be a lot more chill than the average workplace. It's easy not to take your job too seriously when you know the stakes are low, and if you and your coworkers are able to be chill and have fun together, then it might be one of your more enjoyable jobs! You're making a lot less money than you made when you had a full-time job, but you're getting paid weekly, so it doesn't feel like you're short on cash. You can also learn a lot about corporate culture while temping: you learn how heartless it can be.