The RFE clearly specifies priority "10 - Lowest" so I don't see the point of people that downvoted because the issue is very low priority. Indeed it's very low priority but that's exactly what the RFE says, so if you think it's very low priority then you agree with the RFE and should vote yes, in my view.

Not necessarily, as you can (and probably will have) your own order of preference also among the priority 10 items, wanting to prioritize (upvote) some and deprioritize (downvote) others.

Make it so that the PC cannot be sacrificed on the *very first turn* when he steps on an altar on D:48. If he lingers or steps on it again, only then should it be dangerous.

Altars aren't that rare, really. Is it like a 1/10 chance for one to be generated? Maybe even more common? It's really easy for a newbie who's exploring the level for the first time to assume a light gray underscore represents an air rift, or a dark gray underscore is an earth rift or mana or whatever. I just think there should be a safety mechanism here, or just make the rifts more distinctive. Change the ASCII character, or turn the surrounding tiles into colored ones, so that a water rift has 8 blue "." tiles around it etc.

I interpret a down vote as "I don't want this to be implemented at all. Ever".

I guess this is arguable, but definitely this is the sense that most people have used downvotes for in this forum, as far as I know.

I think an RFE for "make rifts more distinguishable from altars" would get votes. But the RFE is "Stop Altar generation on D:48," and it shouldn't.

Um I see the reason to make the difference more obvious, but the "player reaching D:48 for the first time" argument is not it. In fact, you yourself have said the very reason why that's so: players encounter altars, rather frequently in fact. So it's the exact opposite, when they see an underscore, they think it's an altar. If they aren't spoiled they have no reason to even know there are rifts on D:48, much less assume an underscore is one. The ones who can possibly mistake an altar for a rift are rather those who have already been there before, therefore know to look for the rifts, the '_' characters.

Exactly. Right now, one sees the RFE and thinks: "No, this is not the solution, this would be an unneeded non-UI response to a UI issue."

The point is, newb gets to D:48 for the first time, and starts exploring. He encounters a blue underscore, which turns out to be a water rift. He explores further and finds a red underscore, which turns out to be a fire rift. He explores further and finds a gray underscore. It's really really easy to just assume it's another rift.
People might not remember the correct rift colors even if it's their fifth time on D:48, it's not like new players get so far on every other run. It's especially easy to mistake a light gray underscore for an air rift, after all air demons and grues use that color.