Griefing is 'valid' yeah, it is in all online games with any sort of pvp.
But just because you can do something, does it mean you should?
The difference being that IRL there are comparatively bigger consequences, if you are flying a relatively cheap ship, there isn't really currently in Elite.
Personally I wouldn't mind a pvp rating system, nothing big, just a simple quick indicator of the persons pvp behavior, title different icon or such perhaps? that way at least you know when you are in a system with a 'known' aggressive player, should the npc's or such go after that person also?...maybe though personally I would like that to rather be tied into the reputation system, so that if a non allied player, attacks someone that is allied to a system faction's police forces, that are nearby, they will come to defend you, (this sort of happens already?)
Now I know any pvp rep system might not be popular because, well people don't want consequences on their griefing, there are plenty of games out there where this can be seen when changes arrive.
And while you can argue that a game should be 'fun' and those that find griefing fun shouldnt be blocked from doing it, in this case. Elite Dangerous is a simulator, which includes simulation of consequences for your actions.
That said, I don't think anything more direct then above should be added, (like instant arriving police when non are nearby) or such, but there should be some sort of indicator in my opinion, and police should defend their allies from attacking players.