Underlying this, of course, is the now dominant definition of capitalism whereby any restriction to corporations is unacceptable (and immediately labelled communist and thus evil). Externalities cannot be internalised unless the Chinese and Americans do it, and as the Americans are "real" capitalists and don't do it, and the Chinese are, hmm, presumably real capitalists as well, and don't do it either, we should not do it.
It might also be a worry that our products might be outcompeted should we have a tax that others don't. But can't we just go on ahead and place a carbon customs duty on imports from territories that don't have as high carbon tax? A vote for PES is a vote for EPP! A vote for EPP is a vote for PES! Support the coalition, vote EPP-PES in 2009!