Long time lurker, and first time poster. I want to add my 2 cents.
Something that I haven't heard anyone mention is the increased supply of workers if the minimum wage is raised and how it affects current minimum wage earning workers.
If the minimum wage is $8 and it is increased to $15, the quantity supplied of employees will increase. People who for some reason are not in the workforce (stay at home parents, for example) may decide to join the workforce if they can now earn $15 instead of $8 an hour. Since there is now a greater supply of employees, employers will have a bigger pool of potential employees to hire from. For someone who currently earns $8/hr (and are relatively unskilled), they will now be competing with a more skilled and more desired employee for the same job that now pays $15/hr instead of $8/hr. What this does is essentially push out of the labor force the workers who were earning $8/hr, and instead of earning $8/hr... they are unemployed. The people who are supposed to benefit from raising the minimum wage are often times the ones hurt the most.
Labor is a commodity like anything else, and will follow the basic laws of economics. If the problem is that minimum wage workers don't have enough money, then why doesn't government mandate price ceilings for all consumer products (I'm against this too... just a little food for thought)??