Ah yes. Now trying to save the girl from WG is loser behavior? I thought Dragon was a loser for not saving his subordinate.
Luffy declared war on WG for Nico Robin, a woman.
This is a reductive way of framing the issue. These are not very equivalent situations.
Ginny was a commander in Dragon's army, and so their potency as a militia was damaged when she was abducted. On top of being a close friend of theirs. And she was taken to Mary Geoise, not God Valley. A lot harder to infiltrate without losses.
Robin was sacrificing herself to protect the Strawhats while also avoiding her fear of betrayal by them. Emotional and physical shackles that kept her from being "free." The freedom loving Strawhats could never allow that.
Shakky doesn't have those kinds of relationships or reasons (save maybe Gloriosa). She's just pretty. Rocks pirates are all cutthroat opportunists that hate each other. Roger pirates literally stalked and tried to kidnap her. They all just see her as a beautiful object. A jewel, a "crown jewel" even. So it just makes them look like self-sacrificing idiots in service of their lust. Unless you think Oda is doing some lofty metacommentary on beauty bewitching great men and making them lose sight of their ambitions, turning the smartest to stupidest, etc etc. Which at least I get the logic there.
This is of course is all kind of assuming that
Saving Bartender Shakky™ was the cause of the GVI, and not something else.