For new users why give them the option of either setting up so that all users must use the same settings or setting up so that all users have their own settings? The first option is useless.
For those that have some pathological need for awkwardness then the mirc.ini trick exists to fool mIRC into thinking it is an upgrade of an old-style installation. I don't see why mIRC must always provide option after option whenever something changes even if the old way of doing things has no benefits over the new. Why must mIRC meet every user's unreasonable and impractical demands which no-one would even think to demand from any other peice of software.
Running your settings from the installation directory is bad practice, period. The upgrade functionality exists so that existing installations aren't broken by the upgrade, but there's no reason why mIRC should continue to support that bad practice by providing a GUI option - something that would "legitimise" the installation directory method in the eyes of many short-sighted users, whereas if the option weren't there they'd use mIRC happily without ever thinking twice about it.
If you're running as a single user on a machine then it doesn't matter one iota where the settings are kept. If you're running mIRC with multiple users then do you really think everyone wants to use the same settings and scripts and that everyone should have the same access and privileges on the computer to achieve it? Even if by magic all the users wanted to run the same script with the same settings all they need to do is use mIRC's command-line switches on their shortcuts to make mIRC use settings from a folder which all users can access, or you can use the mirc.ini trick when installing as people have stated.
So, why is any of that unreasonable?
