I am a leftist economist and strong supporter of free trade. The reason I support domestic regulation, taxation and redistribution and also support free trade is very simple. I am consistently egalitarian. Te reason I see trade policy as different from much of domestic policy, is that I think that the (not always stated) aim and result of protection is to help US workers at the expense of poorer foreign workers. I would certainly support negative tariffs for imports from very poor countries if some suicidal politician proposed it.

I am against protection for the same
reason that I am against corporate welfare. Even if the market is not perfect, it is easy to do worse.