Griefing really depends on ones point of view. You saying to don't mind it. Then it isn't a problem. Now the player that logs in and they kill him while he it waiting to load in and they do that 10 times and it takes the player 30 mins to get in to actually play or worse yet quits. Well that is an issue. Or the player that is fishing, hunting, treasure hunting ,or some other PvE type game mode that has their back to you. You shoot them cause you are bored and ruin 2 to 3 hours have playtime for them for your own amusement. Why yes that is an issue. Griefers don't care about you or your fun as long as they are amused at your expense . It is an issue and is bullying, which is an issue.
YodaMan 3D's post in Are greifers actually a big issue? was marked as the answer