If you truly believe that, you should stop buying those products. But don’t expect me to want to do the same, I have no hangups about trading with Chinese people, or the Saudis.
I reserve the right to trade with any person on the Planet, as long as that trade is not objectively proven to constitute the violation of someone’s rights. That is the only acceptable standard for any restriction a government may impose on its citizens, none other. Trading with someone who’s government doesn’t agree with your conditions is not necessarily a violation of rights, so an embargo on such nations would violate my rights. I guess at that point the US should embargo itself. 
I would of course support the idea without the embargo, just the free trade league. Unfortunately I doubt there would be any takers for this league (except maybe Switzerland, though they’re pretty shy about getting into any “leagues”, so it might just have to be a free trade agreement, with no conditions whatsoever, and a US commitment toward ending the harassment of their banks). I’m afraid NAFTA, the WTO, and the other bilateral trade agreements are the best one can expect out of most countries, even if the US miraculously became free trade oriented in the near future. (which can’t happen anyway).
Statecraft is not an irrelevant idea, though. Individuals do not fight empires, other empires do. Access to markets is what enriches polities that otherwise couldn’t be wealthy because of their collectivist policies. In addition, only governments secure rights. Individuals can respect the rights of those with whom they immediately trade, but only government can preserve the rights people more broadly than that.
If there were slaves, say providing for %30 of the sugar market, then you could argue that that slave labor - whether you buy from those who employ it directly or not - benefits you via a lower price due to greater supply. Your trading choices can’t directly preserve rights, and you can’t necessarily just invade a country that territorially falls under your government’s control. You embargo slavery. You embargo apartheid. You should have embargoed soviet communism - in which society there was no conceivable way you could claim you were making a fair trade (legal).
You are right about the US, and most of Europe is mixed enough economically, that no trade is possible without some connection to collectivized something or other, despite what private trade is legal in the nation. That’s why I say if there are basic civil rights, and freedom of emigration, you don’t have to draw a line. In the worst case scenario, people who suffer under the collective move, and those who choose not to move always reserve the right to speak out and vote to change the situation. So even if you trade with a collectivist nation, you can essentially conclude that ‘that’s what they want’. Not so for an authoritarian government.
I’m sorry, but we should not be trading with China - there’s all the rest of Asia with poor desperate overpopulation to work for cheap wages - and most of them are more or less liberalized economies, or could with subtle diplomatic pressure, become more so (I’m ignoring SE Asia of course). China is a sworn geopolitical and military adversary. They have a vested interest in trade, but only inasmuch as it is strategic for them. We’re only enriching them to the point where they’ll get enough good technology and infrastructure to go for broke against us. And nearly the whole country are slaves, holding no real rights over their property, and often conscripted into labor.
I could choose to not buy things from China, but nearly most everything is manufactured there (there are perhaps a few cases where the choice is easier), or is affected beneficially for me because of things that other people buy from China. Government protects rights, and I don’t want to trade in a market that depends on others’ rights being severely and blatantly violated. The government can’t set rules for the market, but it can act against explicit rights’ violations. It’s not in ours or anyone’s remotest interest to go on an imperial crusade to impose a strict Objectivist government on top of the world. This is why the government should take efforts to severely restrict trade with countries like China. This is also the best way to stay ahead of enemies of rights. By not letting them benefit from the values they hope to destroy.
That’s the purpose of the league. It’s actually supposed to be a ‘do-it-tomorrow’ realistic policy ideal. Certainly it would never happen, but I’m thinking from the point of view of what might work best. One idea would be just a general policy of embargo against really unfree countries.
Though, realistically, trade with us is probably the only thing that keeps China from going crazy. They don’t want the dollar to collapse, but if we restricted trade, then I’m sure they might start thinking about it.