All things considered the way they're approaching the migration is fine enough - they're only moving specific portions at a time, they're not stopping C++ development, and they're making sure it doesn't introduce regressions. Adopting a memory-safe language for something like a browser makes sense because it completely eliminates that class of vulnerabilities.
The problem is the way they're approaching the code itself. From their wording, it sounds like they're relying on AI heavily for both writing and reviewing the code. Rust has a steeper learning curve than most languages and is very different from C++. They even mention in the blog that their current Rust code looks like C++ code ported over. If they don't take the time to actually learn Rust before adopting it, it'll just lead to security logic issues that their AI couldn't catch because C++ and Rust don't always behave the same way. And that's completely ignoring all of the other ethical/technical issues with AI
How many times do I have to give him the benefit of the doubt though?
First it was the "using they in documentation is political ideology" Github issue, then he publicly defended DHH when people called him out for being a white supremacist, he implied tech companies are discriminating against white people with diversity policies, and he tweeted that he hopes young people will carry on Charlie Kirk's legacy.
If one or two of these things happened in isolation, I could maybe understand giving him the benefit of the doubt as a non-American (for that last one) non-native English speaker. But all of these things taken together? I personally don't think I can look past that.