Will/Entity:
Yeah, perhaps him helping her doesn't totally negate that. Thinking about it further though, it
still seems wierd that he'd stay behind to create a distratction to allow Simmons to get to the portal instead of going along with her though. If the planetary entity is separate from the inhuman (
something I didn't think of initially), I suppose this would make sense without the writers just writing it in as an explanation having people scratch their heads wondering why he stayed behind to create a distraction if in fact him and the entity are the same.
The ritual sacrifices done in the past are perhaps to sustain the entity living on another planet? He lives through the minds and bodies of others to keep sentient and active perhaps. Assuming Will is not taken over, I'm guessing he eventually will be (
or sacrifices himself in the last moment to keep the idealized guy status) putting his and Simmons relationship in the ground permanently and another quirky footnote the on again/off again Fitz/Simmons relationship. Fitz seeing Will as a perfect guy seems like a set-up of sorts for something off-note to happen to Will
(although I'm guessing after Simmons returned to earth) I suppose.
Monolith:
Good point, it might be because it can take inhumans away and exile them on that planet. Or it might be because the monolith can be used to bring back that really bad inhuman, who may want to enslave inhumans.
Then again, the monolith may be used to exile humans as well as inhumans, and the bad inhuman probably wants to enslave humans as much as inhumans, so who knows. Maybe Gordon was just thinking about the consequences for inhumans and didn't care about humans at all.
Another alternative (but it's a stretch): maybe Jiaying was among the inhumans who exiled the other inhuman on that planet, and he's concerned that if he comes back, he'll take revenge on her and anyone aligned with her.
Or it could be just a legend handed down generation to generation until the story became distorted in a way to give a general impression to Jaiying that the monolith isn't necessarily good for inhumans. Perhaps Jaying just heard an oral variation of the tale giving her an impression that the inhuman genes are a gift and an impression that at one point in time this gift wasn't fully realized due to an inhuman being banished by society... I like this general explanation as it could contain any or some of the specific examples you just gave.
Elliott Randolph:
I just realized he's played by the same actor who portrays the crazy artist in Ghost Buster's 2.
I'm guessing the inhuman he was alluding to is the entity sent away. As that would've been in ancient times, I'm guessing Elliott Randolph probably heard the legend second hand from a medieval cult group; the inhuman is probably older than him. He didn't seem to believe in the portal in episode 2 or exactly know it's purpose but did seem to think it wasn't a good thing to have.
Perhaps the Kree at one time built portals to send weapons across space to distant lands; perhaps how they created a galactic empire? Maybe the star wars route they seem to take in the comics isn't the same route the writers have decided to take with Agents of Shield? If this is the case perhaps Asgardians have had to deal with Kree infiltration in the past.
Rosalind:
I'd like to add that I think Malick knows someone but not who was sent back through the portal because of Rosalind reporting it to him. Didn't someone get excited on the plane last episode while going to visit the supposed president saying something about bringing someone back before Coulson jokingly says it's classified?
Lash:
As he's a comic book character I don't think we've seen the last of him. He somehow escapes the containment unit specifically made for inhumans while in his other form I'm guessing. I think the suggestion above about him being in his permanent form now (something alluded to in an earlier episode) seems likely... Although as long as they have Blair Underwood under contract, I suppose it may be easier from a production standpoint to not always be obligated to put him in full makeup all the time.