I agree, and don't think there should be any tariffs.
Having said that, a US store that has to pay sales tax is never going to win over a foreign store that doesn't have to pay sales tax. Even after shipping, the exact same product will likely be cheaper to buy from the European store.
If you buy something from Europe under the de minimis exception, there's no tax applied at all. European countries/companies usually don't tax buyers from outside the EU, and the US doesn't tax it either.
Applying the same tax for both US and international purchases makes sense IMO. This is what Australia does: The sales tax rate is 10% across the whole country, and foreign stores that sell to Australians have to collect 10% tax and send it to the Australian government. Collecting taxes at the point of payment, even for foreign stores, avoids customers having to pay taxes separately when the package arrives in the country.
That's what Australia does too. Since the sellers already had their systems set up to handle it for Australia, it was probably easy for them to extend it to be used for the EU too.