Why shouldn't someone be paid a living wage when they are working a job to get experience? If they aren't what are they supposed to do in the meantime? The reality is that they often have to rely on government assistance to survive, and even then they struggle to even tread water and often can't put away any savings to better their future. If working at McDonald's is to be seen as a stepping stone, we need to make sure that it is possible for people to go somewhere from there rather than become trapped in a job that pays them poverty wages (which incidentally, is exactly what the employer wants which is why labour needs to unionize).
Also, it's great that *you* don't want to work at McDonald's your whole life, but as long as you eat at McDonald's you need to treat the people who work there with respect rather than look down on them. The job may not be glamourous, but aren't you glad someone does it? Not everyone can be a lawyer, doctor, banker or engineer. Someone has to work the service sector jobs, especially now that the manufacturing sector in America has taken such a large hit.
McDonald's makes about $6b in profits annually, they can afford to pay their employees enough to live on.