I'm surprised that you didn't mention Zig. It seems to me to be much more popular than either C3 or D's "better C" mode.
It is “FUD” if you ask why it’s still const by default.
I'd be curious if you could show any examples of people asking why Rust is const by default being accused of spreading "FUD". I wasn't able to find any such examples myself, but I did find threads like this one and this one, that were both quite amiable.
But I also don't see why it would be an issue to bring up Rust's functional-programming roots, though as you say the language did change quite a lot during its early development, and before release 1.0. IIRC, the first compiler was even implemented in OCaml. The language's Wikipedia page goes into more detail, for anyone interested. Or you could read this thread in /r/rust, where a bunch of Rust users try to bury that sordid history by bringing it to light
Makes memory unsafe operations ugly, to “disintensivise the programmer from them”.
From what I've seen, most unsafe rust code doesn't look much different compared to safe rust code. See for example the Vec implementation, which contains a bunch of unsafe blocks. Which makes sense, since it only adds a few extra capabilities compared to safe rust. You can end up with gnarly code of course, but that's true of any non-trivial language. Your code could also get ugly if you try to be extremely granular with unsafe blocks, but that's more of a style issue, and poor style can make code in any language look ugly.
Has a pretty toxic userbase
At this point it feels like an overwhelming majority of the toxicity comes from non-serious critics of Rust. Case in point, many of the posts in this thread