It would cut both ways, as European cars probably don't meet US standards either.
The problem is safety is not a single variable. Improving one measure of safety might decrease another. EU and US regulators simply have different concerns about what is safe. EU regulators are concerned about pedestrian collisions, but making a car safer for pedestrians might make for worse accidents when you run into a Hummer.
There are other factors too, like US regulators test for what happens when people don't wear seatbelts, in the EU they just assume people do (because oddly Europeans actually use the things).