Personally I don't think this can ever be solved except by doing this, the good players want easy kills and lets face it 9/10 times as a fresh spawn someone spares you, you get a gun. Usually you try to kill them, I think it goes both ways and its not just the Bandits fault. My solution is Fresh spawns don't drop painkillers and don't spawn with a weapon, making them less of a threat. And by killing a fresh spawn your "Reputation" goes down 25 points kind of like Unturned, Your Reputation depends on how much cash they drop and effects certain perks like bonus ammunition drop and would slow down health regeneration. So if you go around murdering innocent fresh spawns it will effect you in the long run. The less your reputation the worse the affects but however killing Bandits would add lets say 50 points back to your reputation so there is a way to earn your points back.
I think there should be a fresh spawn timer of 5 minutes and after 5 minutes they are considered a player and can be killed without punishment. Some ways to tell if someone is a fresh spawn is maybe a different skin or like Xavier said a green crosshair when hovering over that player. And this is my last suggestion, on tab next to someones name it should state Newbie if the player has less than 2 hours of playtime on the server, once the period is over in the bottom right it should say Example: Johnny has graduated from Newbie! As a way to notify the server that they have gained another player in their community and should check him out to see if he maybe wants to team.
Of course this wont fix all our problems and it will take some work but I think it will help alot!
Thanks for reading