> Which benefits Mexican workers and by osmosis the US: the richer MX is, the more likely they'll become consumerist, and the US companies tend to sell a lot of consumerist goods.

I was taking a specific example to illustrate why a general rule makes sense. It may be that your view of the specific example might be right, but that doesn't do anything to explain why the general rule isn't necessary. Suppose it's Vietnam instead of China. There's no similar type "osmosis" there. The particular country doesn't matter when you're trying to stop playing "whack-a-mole." At most, your argument might justify leaving very specific countries out while it still makes sense to keep the general rule for everyone else, and lo and behold Mexico wasn't on the list of new tariffs.