You also have to trust the source code, or trust a recent audit, then also make sure the build you have kept it's integrity and matches the audit build.
There are degrees of security between "I personally built it from source using a compiler I personally built from source" and "Xi Jinping is CC'ed a plaintext copy of every message". The allegation here is that WeChat is basically the latter. No one makes any remotely similar claim about iMessage or WhatsApp.
If you have never read "Reflections on Trusting Trust" by Ken Thompson, I wholeheartedly recommend it. It's a short read (3 pages), but absolutely worht your time.
People might've mistaken it for pedantry/condescension? I certainly didn't take it that way (gave it an upvote) -- though I have read that paper, and was thinking of it when I wrote my original comment :)
It was not my intention to be condescending. I legitimately enjoyed that paper (the technical part mostly), and thought it was relevant to what you were saying.
I've found a lot of many interesting articles in hackernews comments and wanted to share one back.
You forgot "I personally built it from source using a compiler I personally built from source with a micro-compiler that I handcoded in assembly on a computer that I assembled from transistors myself."