> But using a language like Ruby or PHP, for instance, doesn't really lead to fewer bugs, or more advanced software, or cheaper software, or fewer security concerns in practice.

Which domain are we talking about? Of course web-based applications have their own problems, but imagine if idiomatic Ruby or PHP code was vulberable to buffer overflows, double-free/use-after-free or format string vulnerabilities on top of the current problems, would you still say that languages don't matter when it comes to software development problems and issues? Essentially, what you're saying is that modern programming languages aren't any more better in practice in said regards than C. Honestly?

Of course no language can prevent outright bad code, but a language, by it's design, can eliminate issues related to for example type safety and memory safety. Consider Rust as an example of this. What this means in practice is that the language by it's design manages to eliminate these issues. Code is less prone to bugs and has no security concerns related to these issues. More time for validating correct behavior and fixing misbehaving parts.

> But we shouldn't be claiming that using a language like Ruby or Python somehow leads to more secure code. It doesn't, and it's dangerous to think that it does.

What on earth am I reading? What are the equivalents to buffer overflow or format string vulnerability in Python or Ruby? How do I execute arbitrary machine code with Python or Ruby if malicious input is given to the vulnerable program?

Still, there is a whole class of memory errors / exploits that you can stop caring about once you have managed code. The tradeoff is obviously performance. Although as java/.net show us, not necessarily too much of it.

Sure, there's no escaping C, but that's mainly because of the investments we've put into it. Same goes for C++, but it's far more manageable from security point of view. Today we have modern languages which are only a tad slower than C, yet which guarantee safety and control. See Ada2012 for example. Also optional unsafe/unmanaged code blocks can really help with maintaining performance in critical parts while keeping the non-critical parts safe/managed. This goes as far as optional garbage collecting for certain objects and manual for others. Flexibility, none of which C provides and which makes C a horrible language in todays world.

If only someone would start re-writing de-facto low-level infrastructure such as kernels(say Linux) and userspace tools and programs(servers such as apache, implementations such as for Python and Ruby, libraries, ...) in something like Rust or equivalent which guarantees both type and memory safety and has strong emphasis on concurrency and encourages immutable state etc.

Maybe one day we simply don't have to care so much about what's "secure" and what's "vulnerable". Because the concept of software vulnerability is destructive. Yes, it employs people, but these people create no real value, they just fight the destructiveness of vulnerable software. They are worthless in ideal world.