Maybe I've just been lucky. I fly regularly --usually about once a month, and very often there are foreigners on these flights. Sometimes even Arabs! Sometimes they even speak their native language! In the last 20 years how many flights have we had hijacked from American airports? Four? Out of how many flights total?
Vigilance is one thing. Paranoia is another. If we start grounding every flight because somebody feels uncomfortable, we're going to have a lot of angry passengers. Believe it or not, there are occasions where air travelers really need to get to their destination!
You are correct. Most people speak their native language when among others of the same nationality...it’s just common sense.