I use a Nolan modular, so you can open and close the front section. That might be a weakness, but they use metal latches so I'm comfortable with it being very nearly on par with a full-face helmet in that respect, but it still makes it possible to open it and take a drink.
I've been in a crash where the helmet (a full-face) saved my life, primarily, and my face, secondarily. It's not that great a face, but it beats a gaping red hole where I used to have a jaw, thanks. I think most people who ride without helmets or with just half helmets simply haven't had their faces rubbed (ha ha) in the fact that they're pretty darn breakable.
Crashes happen, and without a good helmet you can die simply from falling over, to say nothing of coming off the bike at speed.
But of course, the helmet debate is a very infected topic, and I'm trying to steer clear of those I guess.