I think it's just different from what you are used to. After a day or two it is like holding any other metal object. The next phone will then feel "slippery".
I have no problem holding a 6 plus. I think the fear is in people's heads.
I gave it a try and for me it's a no no.
I have a 6 and it feels way to slippery, even after a day or 2.
Might be because i have dry hands or something, but it's slipping out of my hands constantly. I even like the feel better with a case, it's reassuring. I don't like the naked feel of the metal.
I don't agree with you about people just doing it because they think they should. And they do offer significant protection against broken screens. Unless you drop it on it's screen on an uneven surface, or unless it's just a really thin case, generally decent cases will protect your screen from shattering in certain situations.