I understand why many people would want their government to protect domestic industry, but if you truly support capitalism, this is no exception. The reason why I oppose the government taxing foreign imports (protectionism) is that if a different company was providing a product for a cheaper price, I wouldn't want the government to jack the price to protect the other (the competitors.) If a government truly wants to lower prices of products for its citizens and provide abetter economy, it would not do it by stifling competition, which is what protectionism can do.
Working to protect the interest of a society or nation by defining policies favouring to local businesses or societies are called protectionism.
A leader of a society/nation is expected by his/her own people to protect their interest. There is Nothing wrong in protectionism. USA applying dutie on import from competing economies is not wrong if the intent if to create local growth driver in USA.