In a new post to his site Pascal Martin shares some thoughts about why INI directives are evil, mostly in how they could be used to enable/disable major pieces of functionality in the PHP language.
A few times, while evolutions were discussed for PHP 7, someone suggested a new feature could be optional, depending on an INI configuration directive — the idea being each user could then enable it or not.
Still, the idea of directives that could change, sometimes deeply, the behavior of a programming language… It scares me!
He goes back in time a bit to talk about a feature like this that was once a part of the language (happily removed now): "magic quotes". He points out that, while the intent was to provide security to submitted data, the results were disastrous if it was moved to another server without the setting enabled. He also points out some of the steps that have to be taken when a new directive controlling a major feature is introduced - even worse if you're creating a product to run on other peoples' servers.
In any case, before suggesting "but they could allow us to enable or not this feature with a simple INI directive" for ideas as critical as a weak or strict typing mechanism, ask yourself: do you really want two languages with very distinct behaviors, and applications and libraries that work only on some combinations of configuration values?