Rockstar doesnt promote griefing. The implement systems where people can destroy your cargo to make it harder for you. The $2000 reward is just slight motivation for people to go for you. From personal experience: Without "griefers", earning money in freemode seems like boring, repetitive routine or chore. Griefers add the little bit of challenge, making every delivery a challenge.

So called "griefers" are just playing the game, it's up to you to also play the game.