I think that Exxon Mobil owns the responsibility for its business's CO2 impacts and can't wiggle away by saying "we're just servants to our customers' buying habits -- lecture them about emissions." Likewise I think that when Chinese factories make money from CO2-intensive exports they also own the responsibility for the corresponding environmental burden.

Of course Chinese factories may decline to voluntarily erode one of their cost advantages by bringing environmental standards up to parity with e.g. the EU, and in that case I think that the EU should use tariffs to ensure that imports don't get a competitive price advantage by way of externalized environmental damage. But that's somewhat different from believing that shoppers buying imports are really the responsible party when it comes to pollution generated by those goods' production.