Statically typed languages only eliminate SOME things you'd otherwise have to test. In the end, you can eliminate almost anything besides logical errors, however, those are unfortunately a pretty big portion of bugs :D.
So while I would always use statically typed languages for anything that needs to be reliable, I do not see how this is in any way a necessity. You CAN write reliable programs without type safety, you just have to test things you normally wouldn't have to test (i.e. the lack of type safety introduces a whole bunch of null-pointer style scenarios where you get something your code totally didn't expect but has to deal with).
As for performance. Statically typed languages are usually faster, mostly because we do not have the technology yet to make dynamically typed ones as fast (in the general case). Not because there is something inherently different about them.
However, I imagine the technology to make them on par with statically typed languages will take another few decades. Mainly because untyped languages need sophisticated transformations to be fast. That is the job the human normally does for the compiler in typed languages. Things just fit together and play nicely. With dynamic languages, your get one big spaghetti soup with no structure and now the compiler has to figure out the "intended" types and compile for different estimated function signatures, etc. all while honoring the JIT-style performance considerations (fast startup, low overhead during runtime). This is a gargantuan task that probably will require advanced machine learning before it really takes off.
> I do not see how this is in any way a necessity.
Right, but that's not my point. My point is that using a static type language isn't JUST about performance. If I define foo as a string and call it as an integer in my program, my compiler is going to catch it, whereas in a dynamically type language I may not discover the bug until it hits production.
Statically typed languages typically have better performance.
In C, i++ is one or two machine instuctions. In javascript, we don’t know if i is an int, or something that overrode ++ to download wikipedia. So, it ends up being a function call in naive JavaScript. Fast forward a decade, and dozens of PhD theses mean that ++ is usually a machine instruction in JavaScript, but it is not guaranteed.
Two decades ago, dynamic languages were more typically scripted / interpreted, and statically typed languages were more typically compiled. Scripting does allow for quicker iteration (especially if compared to a language with a slow compiler) and compilation usually does produce faster code (at least pre-dating sophisticated JIT compilers).
Uhh, someone please correct me if I'm wrong, but aren't statically typed languages about reliability (e.g. testing, mutability)?
EDIT: in addition to performance, not solely.