Do our Euro friends realize that hundreds of armed passengers fly on U.S. airlines every day in the form of traveling Federal agents and assorted law enforcement personnel? They aren't directly connected in any way to protecting the aircraft (i.e. Sky Marshalls and FFDO's) their flying on?. Their weapon is a job-required tool they have to carry with them, even though most of them never have cause to use them in the performance of their duties, and qualifying with their weapons certainly doesn't involve tactics particular to an aircraft cabin.
The fear of armed pilots despite screening and training borders on the Irrational, no matter the atempt to drape that fear with a facade of rational debate. I'm convinced it's a cultural thing, and never the two opinions shall meet.
Euro pilots should certainly refrain from applying for airline jobs in the U.S., given that their fellow crewmember or some passengers in the cabin may be armed. I would think the fear would create in them a mental situation where they couldn't perform their duties.