According to economists, minimum wages are very bad, especially for lower-paid workers that are supposed to benefit from them.  Here's the reasoning.

In plain English terms, the idea is that if I tell you you have to pay your worker $8 per hour, you'll hire fewer people than if you were allowed to pay $5 per hour.  Imagine if you could afford to pay $10 per hour for your workers.  If minimum wage is $8, you pay one worker where you could have hired two at $5 without the minimum wage.  So that other worker you could have hired is hurt by the minimum wage.

In economic terms, a minimum wage creates a surplus of workers because it makes businesses demand fewer workers (lowers quantity demanded) and it makes more workers want to work (increases quantity supplied).