>Safety not important in HFT? You'd better make sure those precious microseconds buy you enough to make up for when things go awry.

Memory safety bugs are very rare in modern, well-written and tested C++. The key difference is that there are no adversarial inputs, while something like a browser or server needs to deal with potentially adversarial inputs, making absolute memory safety much more important (as even a single memory safety issue could be exploited).