You don't need a screen protector unless you abuse the heck out of your iPhone. I haven't used a screen protector since the early days of smartphones when the screens were fairly soft and you had to use a stylus which often got grit caught under it and would produce huge scratches.
I've never used a screen protector on any iPhone, and never had any scratches on the screen that I could notice. I certainly don't baby my phone. I carry it in a front pants pocket and try to not put anything else in there with it. This is a phone.. not a piece of museum art.
It's the most expensive pocket computer available in the general marketplace, and it just so happens to have a phone app. People who tend to look after things will look after an expensive daily companion like the iPhone even more. I certainly don't treat mine like it's "just a phone". It gets used heavily but it also gets babied. We're all different and I baby everything.