I can't honestly say that it's the generic Kerbals themselves I care about, though I do find the derpy little guys cute. It's more the notion that in order for me to consider my manned missions truly successful, the crew must survive and return home. If they don't, then I've failed. It is a form of RP I suppose, since I obsessively follow a mission plan of probes to a target planet first before sending a manned mission. It's not at all necessary, as you could just build a lander and go straight on... but that's the way it's done in the real world, so that's how I do it. Plus, it adds an additional element of challenge and difficulty to the mission... I do things very differently with manned missions than I would do them with a robotic craft. Fewer risks, more redundant backup systems, LES, etc. That having been said, I have to admit that certain Kerbals -do- have a special place in my heart... either because they were the ones I grew to know since the alpha days, or because they're named after my favorite YouTubers. So I do tend to care a bit more about the welfare of my crew when Jeb, Bill, Bob, Kurt, Scott, and/or Danny show up on the flight roster. Silly perhaps, but when any of them are on board I will go that extra mile to make sure they come home safe.