Yeah but here's something, would you rather use your personal opinions/ideas/views etc. in the way while joining in an alliance of peace up against the world's greatest enemies? It will give the opposing team a very huge advantage and they will win the war. As a teammate of nations, you need to leave those personal stuff behind and focus on fighting for a better life. Now for the Iwa Ninja, if that was a certain issue, shouldn't we see some tension already with them and the Konoha ninja? As of now, looks like everyone is ready and saying, "Hi! I'm Earth Nin, I'm your teammate!" "Hey there!" "Let's team up and kill some enemies!" "Yeah!"
Yeah, and think about Tsunade. Her fiance Dan was killed by ninja from another country (Iwa if I'm recalling correctly) and that death traumatized her for years, but is she refusing to work with Earth ninja? Nope. Look at Chiyo even, while she was enraged thinking it was Sakumo. once they got through to her that it was his son Kakashi she calmed down and worked with him with barely a grumble. Iwa ninja are more likely to make mildly mocking comments about how the "Yellow Flash" must have been over rated to have such a son.
Dream you dream alone is only a dream, but dream we dream together is reality- Yoko Ono 1971
When you go to war, both sides lose totally- Yoko Ono
Remember, our hearts are one. Even when we are at war with each other, our hearts are always beating in unison- Yoko Ono 2009