The show is exploring the theme of immigration through their various dispossessed alien characters – an entirely understandable choice. It’s attempting to convey the message, basically, that there’s no need to be suspicious of refugees, and to treat them with acceptance and tolerance – an entirely admirable decision. It’s not, however, conveyed particularly effectively, because many of these same dispossessed aliens end up being the ‘threat of the week’ – while the episode is saying one thing about refugees, while demonstrating another through its plot. This paradox was painfully evident in the aforementioned episode Welcome to Earth, wherein one of the alien refugees does turn out to be evil, despite frequent insistence that this wouldn’t be the case – it’s a frustrating lapse that undercuts the message that Supergirl is reaching for.
What makes this particularly frustrating, though, is that there are several other avenues open to the writers from which to explore this concept – many of them more effective than the direction they opted for.
Here’s an article I’ve been meaning to write for a little while, about how Supergirl has been handling the themes of immigration. There’s a chance it might form something of a broader series of articles – alongside, I suspect, “Legends of Tomorrow and historical racism”, “Arrow and capitalism” and then something else about The Flash just to cover all four – but I wouldn’t hold your breath there.
(Yeah, I never did do those other ones. Would’ve been interesting to see what I came up with. Ah well. If I remember correctly, actually, I wrote the above post in school during a free period. Those were the days. Anyway, I’ve not re-read the above; I suspect the basic point I was going for still works, but forgive me any lapses borne from ignorance.)