Bad example: Pirates attack NY, one Navy guy kills all of them, then he logs of... so all the pirates can go back to NY and start over again? Nope, I don't think that would be fair.
Simple and maybe a bit dummy example, but you see my point, right?
But on other side, in rarely used systems, I think it's allright to go back when the person who killed you logs off (or goes far away from system)
Then, if you are a trader, that guy shoudn't complain about you being back is system, but I have no clue what you are.
I buy things I don't want to make an impression on people I don't like.