What will an out of state seller get from your state government in return for doing the same?
You've got a point. But by the same token, when a customer pays a sales tax, in return for the tax he gets the support of his state government.
Now when that customer buys on-line, he still is getting the support of his state government, but now he is not paying for it. Someone else must foot that part of his bill.
So it's a mess either way.
That's true, but tax enforcement is the responsibility of the state government. What authority do they have to force an out of state company to assume the cost of collecting those taxes for them?