I find it funny how people feel offended as soon as you leave out the words "some" or "most".
Why do you think that is funny?
It's like they want to be offended or something, don't you think? Isn't it pretty obvious that when someone says "Americans are silly people" they don't mean that literally every single American person is silly?
I'm not sure it's all that obvious. That's pretty much the entire foundation of the very popular practices of "stereotyping" and "racism".