The way words are used in native languages and the connotations they bring up is not easily and fully explained by a 7 word blip in a dictionary... even then, this dictionary claims that must is "should (expressing necessity)": that parenthetical is key to the strength of "must".
In fact, looking at it, you dropped half of the definition you pulled for "should" ("typically when criticizing someone's actions") and I will claim are mischaracterizing what an "obligation" is (just because I am obligated to do something, doesn't mean it is a necessity for me to do it).
Putting this into practice, if you tell someone that they /should/ stop at the kiosk before parking in the lot, normal speakers of English will treat that drastically differently than if you instead say that they /must/ stop at the kiosk before parking in the lot; the former feels subjective while the latter feels objective.
For a rather clear example of this: "you /must/ open the drawer before you [can] take things out of it" would go unquestioned, while "you /should/ open the drawer before you take things out of it" will cause many people to wonder what the alternative to opening the drawer could be.
(edit: I see that chc made a similar complaint about your comment to me 10 minutes earlier, but I didn't see that comment as I was working on mine; I think mine has some value still with the examples, and a slightly different focus, so I will leave it in the thread as a reply.)
In fact, looking at it, you dropped half of the definition you pulled for "should" ("typically when criticizing someone's actions") and I will claim are mischaracterizing what an "obligation" is (just because I am obligated to do something, doesn't mean it is a necessity for me to do it).
Putting this into practice, if you tell someone that they /should/ stop at the kiosk before parking in the lot, normal speakers of English will treat that drastically differently than if you instead say that they /must/ stop at the kiosk before parking in the lot; the former feels subjective while the latter feels objective.
For a rather clear example of this: "you /must/ open the drawer before you [can] take things out of it" would go unquestioned, while "you /should/ open the drawer before you take things out of it" will cause many people to wonder what the alternative to opening the drawer could be.
(edit: I see that chc made a similar complaint about your comment to me 10 minutes earlier, but I didn't see that comment as I was working on mine; I think mine has some value still with the examples, and a slightly different focus, so I will leave it in the thread as a reply.)