the "pro" argument is that it reinforces him as the most patriotic leader available, primarily with nationalists. i agree with you that he's not that stupid, but i believe that he's counting on his audience to either be that economically illiterate, or to be so rabidly supportive of him that they'll go along with it.
to wit, a few conversations with some red hats that i've had:
"tariffs will put america first and make us be more dependent on american-made goods and services"
"but, at least in the near-term, tariffs will also create shortages AND further price increases, which is a major sticking point for you with 'bidenomics'"
"no they wont"
"i'm happy to see that trump is putting america first and seeking to level the economic playing field with other nations. globalization has been a setback"
... (establish that they're talking about tariffs)
"until the us can get up to speed with the raw materials and manufacturing of things that we've traditionally imported from these companies, there will likely be shortages and price increases"
"that is a small price to pay. sometimes you have to make sacrifices to do what is right."
i'll reserve judgment on these conversations outside of the assessment that trump is hoping that the majority of his supporters fall into a category such as one of the two above.