Look, it really does not make one bit of difference if other countries employ protectionism, they're the ones who are losing out on the benefits of specialization and comparative advantage. It would be nice if everyone cooperated all of the time for maximum and mutually beneficial gain but it is foolish to eliminate all gain just because one country's economy doesn't want to reciprocate in all facets. It would be like a salesman -- whom a week ago was diagnosed and properly treated of a potentially fatal disease by his physician -- get's furious with his physician because the physician is making for herself the products the salesman normally sells.
Put yourself in the situation: you were still healed, right? And was it worth the money that you paid to get healed? Can you knock the physician for not buying from you if she can make whatever it is that you're selling, more cheaply herself and that, most importantly, she has the time to make herself.
First of all, the US Constitution in Article 1 Section 8 gives Congress the power "to regulate commerce with foreign nations". This is done so we do not have enterprising capitalists who make a deal today and regret it tomorrow, or worse, become beholden to the countries they sell to.
Trade is a valid function of the Federal Government.