This reduces costs, and therefore reduces prices (through competition). Everybody is a winner (apart from the previously-protected businesses who now have to compete on a level playing field).
Some of those places that are more efficient are more efficient because, hey, they don't regulate emissions. Or they don't have strict safety standards. Or they don't require employers to take care of injured workers.
Clearly, not everybody is a winner.
This is only true when all actors play by the same rules. Without this requirement the most efficient places to operate are where there are the fewest labor and environmental protections. I would 100% be in favor of eliminating tariffs to countries that meet the same standards but its silly to say that we're better off exploiting not-quite-slave labor.
That’s the current situation with the EU. Turns out the UK is not happy with that.
Thank God the Brits have such a taste for irony. They'll be feasting on this one for the better part of a decade.