Let me just say that it is very distasteful when those accuse Supergirl of being political. They are always very clear not to bring up politics. Addressing social justice issues is a comply different matter. The human-alien controversy was just supposed to represent discrimination that we see in the society. So subjects that Supergirl addresses such as: racism, discrimination, transphobia, etc... are essentially just human rights and social justice not politics.
As of now, I think Arrow is the only show that really digs deep into politics if you want to criticize something for being too political.