[@The Mage]Hard Sci-fi is even more niche here.  I think there is about 5-10 people on this site who like hard sci-fi, could be more but I have yet to meet them.  The rest are space opera folk.  That is not to say anything on their quality of roleplaying or story telling, but it is more to say on the creative choices they make usually end up in the space opera territory.  

To give an example,

I actually get bothered when someone calls something that is clearly human looking an alien, it is damning as all hell.  Even when playing space fantasy where alien species are more like races on different parts of the same planet, and that is where it makes the most sense, i'm not going to complain about it in star wars because star wars was always made with the intention of being space fantasy.

The worst offenders in my view are those who try to actually try to act like it is realistic instead of just saying 'it's space opera dude, we aren't trying to be realistic with the aliens'.  

Look, it can't be justified if the setting is sci-fi or there is a alien policy that asks for more alien forms due to the cause and effect over billions of years evolution is.  It is not just having present earth conditions that you need to get humanoids.  It is also having all sorts of events transpire in the way they did on Earth going back to the first cellular life on Earth.  Since usually sci-fi RPs usually are within one galaxy, it is incredibly unlikely to encounter another species which looks so human-like if it has the same facial design as us despite such face being really only seen with humans on Earth.  Even if you seeded another world with humans and baked it for a million years, you'd cook up not elves but likely some humanoid that looks distinctly non-human to us even if it is adapted to what planet you put those people on.  Just look at our nearby evolutionary relatives for what I mean.

Genetic modification is the cure-all to this of course as we would apply our concept of beauty to whatever forms we make so it'd stay looking like us and get the fancy colored humanoids and fantasy races people like making since you'd get people made with the intention of looking like fantasy races by the person who made the genetic coding.  In short genetic modification aligns a lot more with how I notice a lot of aliens are made than well, the aliens they make.

Amusingly enough, there has been times when i've seen genetically modified people in a sci-fi NRP that look more alien than the actual supposed aliens in the setting.  The reasoning for aliens that are remarkably human-like i've gotten are that they don't want to be subject to the limitations humans are given, which has caused me to try finding ways to make humans more widespread in order for that not to be an issue.  You still get humanoid aliens it turns out, even in situations where humans get millennia in space and were abducted in Paleolithic times and placed on other worlds.

Of course RPers want a humanoid form because they're humans, i'm human too so I end up having some degree of anthromorphization anyways especially if I am playing as said alien and not as someone encountering an alien.  Though it does seem like alien in many cases is more a flavor than anything else.