You are suggesting that you are infallible, as the "dead simple errors" you refer to get out into production systems every single day. More than one serious security hole in rails has been due to very similar problems. You are very much implying that you are a better programmer than the entire rails team. And virtually everyone else, as examples of these kinds of bugs are everywhere.

And finally, crying straw man while presenting a straw man is poor form. If a particular library has a deficiency, that's unfortunate. But it has absolutely nothing to do with type safety. Haskell for example is more type safe, and it has two http client libraries, both of which provide safety while also allowing arbitrary headers (and methods, etc).