It is fallacious to pretend erlang is slow because otherwise you have to write bad, unoptimized C code. First of all, unoptimized C is still an order of magnitude faster than erlang (or more!). Second, there are other languages besides just erlang and C. For example, compared to erlang I can write the same thing in haskell instead, have it written faster, have fewer bugs make their way into production, and have it run faster.
If your C code is doing linear scans over arrays where a dictionary style lookup is really needed, then there is no way in hell the C code is going to beat the Erlang code. I've seen this again and again in C programs.
As for your Haskell program, you are right. But you will spend the next 3 months trying to fix memory leaks due to lazy evaluation :)
I think the bottom line, one we can agree on, is that a program written is not the end of development. It needs maintenance and where certain programming languages makes it easy to do something, other languages have a harder fare, and vice versa.
Erlang has a state-of-the-art interpreter. And a runtime written in C. It is not a slow language if you have a program that spends most of its time waiting for other things to complete or in the runtime. In fact, that is where it shines.
That said, don't write CPU-bound jobs where constant factors matter in Erlang. It is a bad fit for this, because of its interpretation overhead.
So now we're not just comparing optimized erlang to unoptimized C, but optimized erlang doing X to unoptimized C doing Y. You can write the wrong code in erlang too, C does not have any special (mis)features that encourage doing the wrong thing. It dishonest to say "erlang isn't slow" and use "I can write slower C code if I do it on purpose" as evidence.
The thing is that "slow" is naturally relative. I hate it when people claim that a tool is slow. By far the most important factor in getting programs that work isn't the technology but the mind behind the code. This is true for any programming language.
I guess the succinct answer is: No, Erlang isn't slow if you know what you are doing, barring the Caveat about CPU-bound problems. The message I am trying to convey is that there is more to fast programs than the execution speed of the technology at hand. It is a factor, admittedly, but it is not the sole factor.
