[yontherubicon]

>it pisses off trade partners who may not act as rationally as you expect

It forces trade partners to lower their own protections, resulting in freer trade than before. People respond to incentives.

>it might not be possible to manufacture an iPhone without cheap labour

Automation.

> Also manufacturing jobs are crap.

Manufacturing provided decent jobs for many American men feeding their families. Next you'll tell me that trucking is terrible and we should get rid of that too. Schumpterism is probably a necessary trait for ambitious people, but don't be cavalier about jobs that provide respectable livelihoods to normal people.