One problem with the general lower standards argument is that it is so open ended. Based on that, the world could quickly slip into outright protectionism hurting everyone along the way. Sweden could slap massive tariffs on US goods based on low social and environmental standards or even currency manipulation for instance. Measured by purchasing power, the US dollar is about as undervalued relative to the Swedish Krona (and many other currencies) as the Yuan is relative to the US dollar.
Also, we have been importing commodities from brutal dictatorships for decades or even centuries in order to fuel our economies without ever complaining about low standards. Now that these countries start competing with us we're suddenly up in arms.
But ethical issues aside, such tariffs just make very little practical sense. Helping US and German panel manufacturers and at the same time hurting installers, equipment makers and consumers isn't going to help. Surely, the Chinese will retaliate.
Effectively, the Chinese and the Germans are subsidising everyone elses cheap clean energy. Let's just use it!