Robin is as much apart of this war as everyone else. She's also been able to avoid being captured for over 20 years on her own merit, long before she ever joined the Straw Hats.
Is every enemy on Onigashima just supposed to stop what they are doing and who they are fighting to run around and try and capture Robin? They wouldn't have to look hard because Robin hasn't been hiding. She's been out on the frontlines fighting. People knowing where Robin is doesn't mean anything, because she's a big girl, and can take care of herself. Notice how the only Straw Hat who commented on Robin being wanted, was Jinbei who doesn't know her as well as everyone else. Not a single other Straw Hat was worried, because they all have faith in Robin. Jinbei will learn soon enough.
So to sum it up, i grasp these are your points:
1. Robin is experienced in such battle
2. Robin is already in the frontline and nobody is capturing her
3. Jinbei doesnt know Robin well enough
I agree with your third point, now let us see your first two points
For your first point, it still doesnt justify such act, just because you're experienced you can't act recklessly, Sanji knows very well that the world want Robin so bad, and Sanji knows it as well that they're fighting a Yonkou crew, i repeat, this is a yonkou crew that they are fighting against.
As for the second point, true, Robin was already in the frontline, so there are several possible interpretations why didnt the BP target her in rhe first place, as follows:
1. The BP doesnt know/recognize Robin's face
2. They do know, but somehow they didnt try to capture it as if they're blind
If we want to make this logical, the first option is surely the most logical, if we want to talk without PIS, option 1 is definitely the case.
Therefore, your first point too doesnt justify sanji's act. In addition, just because Robin is already in the frontline, Sanji shouldnt make the situation worse. if something is already bad, you are expected to make it better, or lessen it a bit, not making it worse