I think the mistake you're making is that the protectionist policies of (say) the US and China are not remotely comparable. In particular, the whole reason the US needs steel and aluminium tariffs is that China has used protectionism and state subsidies to build a steel and aluminium industry so far in excess of what the country consumes that the surplus has tanked global prices. This is pretty much unprecidented. The US is not the only country that objects to this; the EU wanted to put tariffs on China a few years earlier but they couldn't agree on which goods the tariffs should apply to.