IME, open casket funerals are the exception, but usually there’s a ‘viewing,’ usually the evening before the funeral, that is open to anyone who wishes to pay their respects.
Ghastly custom, IMHO, on multiple levels. First, why should anyone besides close family members even have the option of seeing the corpse? Second, if you’re a close family member, you’ve got to spend this evening chatting up more distant relatives and friends of the deceased. Swell, huh?
To me, the key thing about the corpse is that it isn’t the person anymore. That person is either somewhere else, or nowhere anymore, depending on your belief system. But they’re no longer inhabiting that body, and to me, there’s something fundamentally revulsive about prettying up the body as if they’re still there. They’re not, they’re gone, and while I know nobody’s actually pretending otherwise, that’s still what it feels like to me.
I don’t want to be looking at this thing that looks like, but is fundamentally not, the person I cared about. Just creeps me out.
ETA: Thank goodness none of my grandparents died until I was in my twenties, and my great-grandparents died when I was too young to remember. So no appalling childhood experiences having to do with funerals and viewings.