Not moral, but some would say being a single country imposes a certain practical requirement that the taxes not be too complicated, if we agree commerce is a good thing and waste is a bad thing.
The United States of America is, in the terms of other countries, 50 states that have given up certain powers and responsibilities to a federal government but retain their own powers, including the ability to set tax policy inside their own borders.
The Commerce Clause gives Congress the power: "To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes." This has been widely construed as meaning that states cannot make taxes that affect other states' citizens unless they are doing business in that state.
The Supreme Court has just ruled that their earlier ruling (that Store A had to have some physical presence in State S in order for S to require A to charge sales tax) is wrong, and no such physical presence is required.
More importantly, it is now clear that American States can tax non-residents, even FOREIGN non-residents who have no connection with the U.S. whatsoever. There will be collateral consequences to this decision. For example, why should I have to pay out-of-state university tuition if I became a state taxpayer due to the sales--and soon to come other--taxes? Drive a car into my state? You have to pay a roads tax. It will be interesting to see how far this goes. Long-arm jurisdiction will become more robust, at the least; another rationale for diversity jurisdiction is removed.
Congress has the ability to nationalize sales tax collection and remittance for online purchases. In fact, there have been bills introduced in the past that proposed to do just that.
We might actually see some movement in this direction now.
It looks like people are downvoting @dsr for, I dunno, being a pedant or something, but I think their point is important: Americans really do seem to value the extreme heterogeneity, and even outright waste, of having 50 different jurisdictions to do business in, rather than passing uniform laws at the federal level.
Although I do agree that in this case it's a bit of a disaster and going to be a huge pain, sometimes it is nice having 50 different jurisdictions.
Most things are pretty similar state-by-state, but it can be really nice being able to pick your laws if you have to. Maybe you love weed and you want to pick a state with legal weed. Or maybe you like drones and want to pick a state with fewer drone laws. So many things differ state-to-state, from REAL ID to trans rights to surveillance to taxes to guns to driving age to social aid to public transit. Gay marriage, slavery, and interracial marriage were all issues of the past but they were very important in their day too.
I do think it's an important part of what makes America America, and being able to "pick your laws" is an amazing freedom that most people don't have.
Now, the actual ability to move wherever you want can sometimes be limited. If you're in Vermont and you want New Hampshire laws, well, that's easy. (Differences: weed, guns, advertising, taxes, many more.) But if you're in Maine and you want Hawaii laws, a move like that probably isn't doable. Still, I think it's a valuable freedom.
The Commerce Clause gives Congress the power: "To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes." This has been widely construed as meaning that states cannot make taxes that affect other states' citizens unless they are doing business in that state.
The Supreme Court has just ruled that their earlier ruling (that Store A had to have some physical presence in State S in order for S to require A to charge sales tax) is wrong, and no such physical presence is required.