The reason for minimum wage is to ensure fair wages. This is important. However, every part of the nation has a different cost of living; California is more expensive than Ohio. It does not make sense to give each state the same minimum wage.
Also, as we raise the rate of minimum wage the cost of living will increase everywhere to make up for the increase in pay of employees.
Having a large gap in wage gives incentive for those that have limited education to get an education. Education is accessible for anyone that wants it, especially with the loans, and scholarships available. Finally, raising the minimum wage will only touch 4.3% of the nation. Employers will want to hire less people, and have more educated people.
This is America, if a person wants something enough they can get it.