This is like saying just because China and the US act much in the same way (for example, they are the leaders in environment pollution) there is no distinction

This is like saying just because China and the US act much in the same way (for example, they are the leaders in environment pollution) there is no distinction between people who believe in a communist regime vs. in a democratic government. Of course a distinction between Republicans and Democrats is useful. For example it is a good prediction to say if you have a PhD, you are probably not a Republican.