People arguing against it say that a sales tax is regressive, that is, it hurts the poor the most - as poor people have to spend their entire paycheck to survive, while rich people will only need to pay tax on a small percentage of their income and the rest can be invested or saved tax-free. Poor people would in effect, be paying taxes on 100% of their income, while rich people would have a much larger percentage of tax-free income.
Proponents of a sales tax argue that it puts government spending in direct control of the people. If a war is unpopular, then the people can regulate the amount of money the government can spend on it by speaking with their wallets. By buying less, the general public will stop the influx of funds the government has to spend on a war. There is also a moral argument, as paying a sales tax means the individual is still in direct control of 100% of his income, and is not forever in debt to the government whenever he decides to be productive.
There are still plenty of in depth factors, but I just wanted to present both arguments simply and quickly.