100% in agreement over the inanity of the term "shmup". It is baby-talk for a mentally-challenged pigeon. Now, "shooter" and "shoot-em-up" are only slightly less imbecilic, but they are certainly preferable.
I spent my whole life using "shooter" and, yes, I would always have to clarify "like Galaga or Gradius" so folks didn't think I was obsessed with Hogan's Alley...but I have had to accept that "shoot-em-up" (which, I am pretty certain, was originally used to describe any carnival/fair/arcade mechanical shooting games—yes, with metal BB's and the like) and "shmup" are here to stay. And yes, I will admit that in today's world we need precise categories (sub-genres) to describe all the different types of games out there.
I just wish we had a term that was more dignified or, at least, more "neutral" (think "platformer").
Oh, why did I waste my time posting this rant again?
I use the term "shmup" in my own writing, too, because I want folks to find stuff that is relevant to their interests.