[Steve is just naturally wary. He focuses so much on the job that sometimes he just can't take things without that rain cloud overhead.]

You said that your EMP approach isn't a complete solution and that there's some kind of magic force working with it. What if using an EMP repeatedly allows that magic element to develop a work-around? Knocking it out just seems like a short term solution.

[Guess where he learned that from? Tony can probably tell that Steve's understand of what he's concerned with is pretty basic, but he knows that they'll need more than an EMP charge.]