Like many others on this board, I travel somewhat often from the Schengen zone (Brussels, Amsterdam, Paris) to the UK and routinely do not receive a passport stamp on entry to the UK. It is not difficult to get into the UK or a non EU country with a US passport.

You can tell how big of a problem it is by the fact that the State Department website has a section saying:
**
Make sure you receive a stamp in your passport when you enter and exit the Schengen area.**
Traveling In Europe
travel.state.gov
This is just like him bombing those empty runways in Syria...This stupid motherfucker is going to get people killed for no reason.