The main argument against the minimum wage is that it may increase unemployment for unskilled workers. However, recent empirical work suggests that the minimum wage is currently low enough in the U.S. that raising it has quite a small effect on unemployment. Therefore, some economists feel the redistribution effects are worth a small cost in efficiency. Here is a survey of prominent economists on the effects of raising the minimum wage to $9:

http://www.igmchicago.org/igm-economic-experts-panel/poll-re...

Many economists would argue that increasing the EITC would be a better way to help the poor.