I have found a fix for the crash on startup issue (Atleast for myself)

[RealAhmed]

This might only work for me, but worth a shot for everyone else too

Backstory: I wanted to play Rust, but it always kept crashing no matter what i did, so i gave up. It gave a crash log whenever i tried to launch the game. It had something to do with steam64dll causing an access violation.

I also wanted to play Unturned for a few days now, but whenever i tried to open it, it opened up for like 3 seconds, and then just closed with no message at all. I have been looking for a fix for some time, and none of them worked, until i tried again today, and the guy said he deleted everything in the "Steam" folder, except

steamapps
userdata
steam.exe

Don't delete the entirety of Steam/reinstall, just delete everything except the things above

Then after you deleted everything except those, just start up Steam.exe and it should reinstall everything by itself.
I tried to play Unturned, and it actually launched and i could play. I remembered a bit later that the error had something to do with steam64dll, so i tried to launch Rust again, maybe i'll get lucky, and it turns out, it did launch. It worked for both Unturned and Rust.

(This fix might not work for everyone but like i said worth a try if you didn't try this before)

[Rustafarian]

Thanks, but this didn't work for me nor did I expect it to. But like you said, worth a shot. My issue is that right before I'm about to load into a server, the game crashes leaving me with a blacked out background and and error message that reads, " RustClient.exe - Fatal Application Exit......Untrusted system file (C:\Windows\System32\iertutil.dll). Now, my initial thought was to just delete it, but I'm not fucking around with anything in System32's folder. I've done so well enough in the past with Windows 7. It only leads to further frustration. Again, thanks.

[TotalLoser]

It did not work for me and I was receiving this as my error crash message upon opening the report.

Rust [version: Unity 2017.1.3f1 (574eeb502d14)]

RustClient.exe caused an Access Violation (0xc0000005)
  in module RustClient.exe at 0033:e9ecf27f.

Error occurred at 2018-05-06_165254.
C:\Program Files (x86)\Steam\steamapps\common\Rust\RustClient.exe, run by ROBINSON91R.
53% memory in use.
7645 MB physical memory [3526 MB free].
8861 MB paging file [4457 MB free].
134217728 MB user address space [134217137 MB free].
Read from location 00000020 caused an access violation.

Good try but this is not a fix for us.