Rule No.2 - always proofread before hitting send/post :)

[EDIT Re your main point, now that the typo is out of the way]

There are various ways of structuring an argument - as a dialogue, as thesis, antithesis then synthesis, or treating it as an oration like Cicero's with 6 parts ending in a peroration. All of them are imposing structure on thought (and thus restricting creativity), and none of them will perfectly fit any argument, but some structure is vastly preferable to no structure at all, which is a far more common problem. The problem most people have in their writing and speech is a lack of structure, and I think the school lessons you evoke are meant to counter that by imposing some (even at the risk of making essays boring and formulaic). I don't think the intention is to forevermore make everyone write in the same structure (which would be a procrustean bed as you mention), but more to show people that you can use structure, and employ it persuade and explain. Students are then expected to grow out of that structure later or explore other possible structures.

Once you understand the mechanics of argument, you can then break them with great effect, but only if you do it sparingly, and it's best to know the rules in order to know when you're breaking them.

A far more insidious problem nowadays in terms of imposed structure is the habit people have of making a list (as the OP does) as if this is a substitute for properly structuring their thoughts - to me that's a cop-out and not far above no structure at all. Usually the results are then labelled top n x or n things you didn't know about x and contain more than n examples of x, without any attempt at an introduction or a conclusion.