While I won't lump those particular idiots in with the entire fandom, this is basically a reason why I won't ever get heavily involved with the fanbase. Being as I'm anti-sub, I havn't yet seen the whole series, and don't know what kind of awkward pairings the heavy duty fanbase have put together. I might do a cosplay somewhere down the line ( as a matter of fact, I KNOW I will. Austria, America, Latvia, deserted island Japan, and or Canada ) but I will avoid the photoshoots as all I hear is about how hectic they are.
As aforementioned, I have not yet witnessed the whole series, so I have no idea whether or not Germany has done any "salutes" or anything of the sort. Even so, just because it's done in a CARTOON doesn't mean it's right in the real world. There will definetly be people of the jewish faith walking around by chance. They're human beings just like us, and can attend conventions/view anime just like us. So yeah, DEFINETLY not a wise choice on those cosplayers parts.
As far as the whole flag thing goes, yes, only soldiers and "true" patriotic people are going to know/feel that the flag on the ground is disrespect. If that's the case, then why not politely ask them to pick it up off the ground? My dad is one of those patriotic people, to the point where he stopped the car on a drive home once, and made me get out and get this window flag that was sitting in the middle of a road ( that thankfully wasn't busy at that moment ) But if you're going to complain about it in private, then you really shouldn't be getting mad. Have a problem with it? Bring it up with the person who's doing it. I'm pretty sure they're not going to say screw you and take a leak on/burn the flag. Now THAT'D be pretty downright dirty. Cosplayers are going to continue laying flags down on the ground if nobody is there to tell them that its a tad bit harmful. But again, chances are that they don't mean it in that way to begin with. As a matter of fact, before I even knew what Hetalia was, I saw several people carrying the flags, not ever once laying them down.