One thing that troubles me about Dr Who/Science Fiction in General

[zarus tathra]

There aren't really any "good" alien races. I think a large part of this is because truly alien races are really, really expensive to depict, and "good" people take up most of the screen time.

[Hydra009]

From the title, I expected a far more serious flaw than just the lack of benevolent aliens.  Since Doctor Who is centered heavily on alien invasions, it makes sense that we'd be far more familiar with the invaders than non-invading species.  But even in that show, non-hostile aliens do exist.

And depending on the show, a large portion of alien races are pretty friendly towards humans.  Trek probably has the highest proportion of friendly aliens (Humans and aliens are integrated into a single political entity - an interplanetary federal republic - which is generally on favorable terms with most alien species), followed by Babylon 5 (Earth is on friendly diplomatic terms with most alien species most of the time), then Stargate (humanity is regularly aided by several alien races), then Farscape (humanity is unknown to most alien species, and except for a few very belligerent species, they don't particularly care about us one way or the other.  But if contact was made, they'd find our culture confusing and we'd likely be far more hostile to them than the other way around.  That was one of their better episodes, imho).

There are far bigger flaws with regards to aliens.  Planet of Hats (the species has a single trait that apparently all individuals embody.  i.e. no diversity), single-biome planet (the planet has only a single climate), aliens that are strangely human in their psychology and sociology (i.e. they think exactly like us, display the same kinds of emotions, have societies and social institutions almost identical to ours, etc).  Actually alien aliens are a rarity.  Mostly, aliens are just stand-ins for human cultures.  Because the show's not actually about aliens, but humanity.

[stromboli]

Stephen Hawking made the point that meeting an alien race may not be a good thing. My personal thinking is that if some advanced race was aware of us, like any good scientists we are merely being observed. Any species advanced enough to travel through interstellar space would probably view us with about the same interest as we view a tribe of chimps, or even as studying amoeba under a microscope.

Contrariwise if any alien race had those abilities and hostile intentions, the scenario wouldn't be like Independence Day, it would be more like smacking a fly.

[Hydra009]

Whatever relationship we would have with an alien race would be either curiosity or indifference, not belligerence.  Space is so vast and there are plenty of unclaimed resources to go around that we'd likely never have a war over territory/resources.  But whatever contact we might have would almost certainly be through probes or ancient transmissions, never face-to-face or even in the same vicinity. It would be a very long-distance relationship.

[Gawdzilla Sama]

The Arisians were good.

But I sort of identify with the Eddorians.

[stromboli]

The Arisians were good.

But I sort of identify with the Eddorians.

Yeah. Good ol' Doc Smith and the Lensman series. I'm old enough to have read them.

[Gawdzilla Sama]

Yeah. Good ol' Doc Smith and the Lensman series. I'm old enough to have read them.

I read them in the '60s. I recently downloaded the whole series, saving them for a convalescence.

[Solitary]

I think the original War of the World's alien and flying ships looked more alien than in any other picture.  Solitary

[Mr.Obvious]

As a kid I once read 'Coriolis de Stormplaneet', or 'Coriolis The stormplanet', as it would be called. In it, you read as an alien sort of shaped like a big puma but with a hooked tail (named Kazazi). The thing was that she discovered two crashed human travellers and one of them was 'evil'. Her species wasn't really and she surely wasn't.
But also in Star Wars: Wookies, ewoks, gungans ... I think it may be a bit of stretch to say there are no 'good' alien species.

[Gawdzilla Sama]

Ring World and the Well of Souls.

[Jason78]

There aren't really any "good" alien races.

The Furlings.   Stargate SG-1.

[stromboli]

The Vorlons on Babylon 5.

[Jason Harvestdancer]

If the Sci-Fi is in television or movies, of course it will have humans, human-looking aliens, or humanoid aliens.  It's easier on costuming and special effects.  If the Sci-Fi is in novel form, then you can get some interesting aliens.  Although Piers Anthony is only a good writer, not a great one, I loved the alien species he described in his "Cluster" series.  The Polarians were absolutely brilliant.  But he didn't need to worry about how to show a Polarian on television.

At least Doctor Who tried to come up with a rationale for this casting preference.  The show explains it with this bit of hand-wavium about a morphic field.  Since the Gallifreyans were the first intelligent species, they helped shape how all other intelligent species in this corner of the universe would appear.

[Jutter]

There've been the likes of E.T. Starman and Close Encounters of the 3rd Kind, but generally yeah... but for understandable reasons I think. You want a protagonist who the audience can relate to and sympathize with, so that'll likely be a human(oid) leaving the antagonist-slot open for the aliens. Few break that mold.

[aileron]

There aren't really any "good" alien races.

I don't follow Dr. Who, but there are good alien races in the genre.  The Vulcans are benevolent.  The Gentle Giants of Ganymede evolved on a planet without predation and lack the aggressiveness of humans.