Why doesn't the US have the freedom to choose what commerce they want to engage in?

You have that freedom: if a company does something you don't like, you go to their competitor. You would (rightly) be outraged if the cops showed up and forced you to spend money at a company you hated.

Why doesnt china have the freedom to choose what commerce they want to engage in? If the US didnt want the chinese selling HP servers to Iran, they should not have sold them to China. If China jailed Tim Cook for selling iPhones to Taiwan that were intended for export to Europe, the US would rightly flip out.

China does have that freedom. The difference is, Tim Cook didn't sign any export control documents, and as of current, they don't exist. In the US the export control documents do exist, Huawei was a signatory as part of parting in the American Economy & Commercial sector. So this analogy doesn't make sense.

Just as China doesn't allow Western products in their markets without a substantial consideration to China, usually in the form of joint partnerships with domestic companies vs direct sales. That's their right, the western companies wishing to engage in the market often times will find out their cost / benefit and act accordingly. All of the companies are held and managed under Chinese law and as such many have had things stripped from them.

A rather hyperbolic comment. We don't do business with Iran- simple as that.