Yes, I am frightened by people attacking political rallies, especially when waving other country's flags. What is so strange to it?

Try to get out of your USA bubble of thought. I live in Poland. Let's say there is a presidential candidate, who dislikes Russia and is in favor of tighter integration with EU and stronger defense on east border. Now imagine that his supporters are attacked on rallies by people waving Russian flags, chanting "Russia" or "Putin". Why wouldn't you be afraid of them? I would want them out of my country.

We can spin it some other way too. For example suppose that after Snowden revelations (top European politics' phones tapped by NSA) Angela Merkel says she won't have any more of this USA bullshit, but her supporters are attacked on a rally by Americans chanting "USA USA USA" (or "NSA NSA NSA") under American flag. Still cool for you?