i am not by any stretch of the imagination- a designer-
(so take this w/that in mind)
stupid is not the word i'd use-jarring- perhaps?
i think- if you put just the front piece on w/o the sides- you get a sudden break in body flow from the front to the back- IE- look at the outside corners of the front piece- see the big blocky corner set up there? the eyes follow that to the matching lines of the side panels included w/the kit. our stock sides dont have those hard defined lines like the kit has.... and on that same note- notice how you never see a true side picture of a car w/that set up? i think that the jarring translation of front end on car w/o side kit- translates the same way from the side to the tail end.
looking at the tail end of the side kit- same blocky aggressive style as front corner- but looking at the sides of the ends of our cars- they are kinda rounded...
but then again- thats my non-professional opinion of it
if i had photoshop skills i'd show you the results and highlight the above points mentioned