I do not assume that the US will continue to be a reliable trade partner going forward. Your logic works in a world with rational actors, where trade between Europe and the US is desirable. However, with Trump as President, the US is clearly ceasing to be a rational actor. It is desirable for the EU to cut back its dependence on the US. It would be bad for the incoming administration to be in a position to coerce Europe through economic means.
Also, by failing to control its monopolistic enterprises, many US tech companies are trampling over the rights and privacy of EU citizens. It is desirable for us to cultivate homegrown options, rather than continuing to let American megacorps walk all over us. Reducing trade volume is a rational choice, despite the short term economic pains.
There are political arguments for tariffs. I don’t think your economic arguments are likely to persuade too many. In a more rational world, I’d agree with you. And I do very much regret that it has come to this point where I’m in favor of protectionism from the US.
I don’t see a fundamental difference, only that “reactionary” is favored more by leftists, and “regressive” more so by liberals. I myself would use the two interchangeably, depending on the preference of the person I’m talking to.