You shouldn't, only Failware should feel bad. This is a game, if players can kill they have the right to and enjoying it is the whole point of the experience!
I remember a term from Non-carebear PvP games, "red = dead", now its "pvp on old the republic = dead"
It's Red = KoS (kill on sight)
Meh, i already gave up with MMORPGs as pvp games. They just plainly suck, most of them are warzone/battleground based, and they don't even work a little to make them really work (balancing classes/roles/matchmaking before the game even starts). Over the years, and playing other games which are not MMORPGs, you see how It's a watered down PvP experience to catter PvE'rs who enjoy carrots.