But the result is the same. It becomes impossible to invest in the EU.
If they refuse to take measures against unfair competition (tariff for the firm manufacturing in the EU, but no tariff for the firm manufacturing in the US), then they're throwing you under the bus and it's not an acceptable use of resources to manufacture there.
You can't trust someone who isn't willing to protect your investment.
Really? If you invest in the EU, you can import the raw materials at whatever they cost, and sell your goods to the world. If you invest in the US, you import your goods at cost + 15%, and can only sell to the US because elsewhere your goods cost 15% more than those coming from the rest of the world.
If it was a VAT, that doesn't happen because everyone gets to claim the VAT back on the cost of goods, and exports don't have VAT levied. But this is a tariff.
We can't assume that the US will hamper its industry for no reason, or that its raw materials industries will forever be inefficient.
That's impossible. Goods manufactured in the US will cost way more than that. The minimum wage in Vietnam is under $1 USD per hour, while in the US it ranges from $7.50 to $15 USD. So unless the product is manufactured by robots (which defeats the point of tariffs), products manufactured in the US will be around 10x more expensive than those manufactured in Asia.