Of course, there's a balance to be drawn and when my players get hit by a ball I know they're as much shocked and scared as they are hurt. And it hurts plenty. That's something that I always acknowledge and validate with them. But it's usually not damaging and that's kind of the distinction. Learning to deal with painful things that aren't really injurious. Not more than a bruise.
That's actually an extremely valuable lesson -- that, although you might be doubled over, clutching your shin, yelling "Fuck! That HURTS! Fuck!", it's not going to hurt that badly for very long, and lo, you'll survive.
But so much of baseball coaching is about teaching them how to handle their fear. It's a legitimate fear, but you have to master it if you want to play.
Plus, once you've taken a line drive to the shin -- at least, this is true for me -- you're less afraid of it happening again, because at least now it's a known factor. You know it'll hurt, and you know how much it'll hurt, and that if the ball takes a weird hop, yeah, it's gonna hurt, but you'll survive.
Because you can't have ballplayers who do that thing where they stick out their glove tentatively while turning their head away, because that way lies missing teeth.