To make it clear, I don't mean to rag on C, which is a great mid-level language. It's the ++ that I hate. Assembly is infantry: can do a lot of fine-grained work, but limited to about 5 mph with equipment. C is a tank-- a pretty powerful and impressive machine. It can shoot on the run and do 50 mph off-road. High-level languages are airplanes, perfect at 500 mph but coarse-grained from an operational standpoint. C++ exists because someone saw a tank and a plane and said, "I'm going to put wings on a fucking tank and see what happens." Thus, the tank-plane was born. The wings destroy its maneuverability on the ground and the weight of the tank makes it a shitty plane, and it looks fucking ridiculous, but there you go. Java exists because someone else concluded that the problem with tank-planes was that people were trying to fly them too fast and built an equally ridiculous invention-- the tank-icopter.

After I have defined a high-performance algorithm, they often want to modify it to make it "more beautiful" (which means functional) and in the process destroy the performance.

That's annoying. They should understand the concept of interface as separate from implementation. Implementations are allowed to be (and sometimes should be) ugly if performance concerns merit it.

Besides, mutable state, intelligently used, isn't "ugly". A lot of programs are simpler and more attractive when mutable state is used. Mutable state just needs to be used with taste.

What really pisses me off about that behavior pattern is when the tinkering is unnecessary. If it's working code, then who cares? I'm a hard-core FP advocate but I write stateful programs all the time. I try to wrap them behind interfaces that are as functional as possible. I will use state in controlled ways when appropriate; I just don't want to impose it on other people.

I work on low-level algorithm design in A.I., where performance is everything and there are many interlocking, low-level and complex algorithms and data structures.

I think what makes C++ appropriate for your purposes is that once code is written to spec, it doesn't need to be maintained (except for performance optimizations). I'm guessing that (except possibly for some STL usage) you're actually C.

Where C++ and Java really drop the ball (legacy disasters) is when code has to be read more times than it is written. If your goal is to write fast software one time and, once it's working code, never need to look at it again, C++ is probably appropriate.