Auto-Attack!

[rrgg]

I just realized something, this already is in the game! It's what berserkers do. (Why the heck are berserkers the smartest troops in this game?)

All CA or modders need to do then, is figure out how to turn it into a toggle-able ability for everyone and remove any moral or combat buffs.

[Greve Af Göteborg]

Perhaps it is possible to toggle the disciplined attribute via a button. If it's the disciplined attribute that does this.
However if it is the "berserk" attribute that does this it'll be a bit more problematic, because the berserk attribute also makes it impossible for you to give orders to the unit and allows the unit to attack friendly units.

[rrgg]

You're thinking of elephants. Berserkers won't actually target friendly troops. What's more you can still select them while they are berserking and use their special abilities, so if it was a toggle button it would be easy to turn off and on.