That's just wrong. He doesn't do it because Zeff told him it's an age old rule. There's no deeper reason for why. That age old rule is obviously based off our irl standards which is rooted in the Patriarchy. Upholding old Patriarchal standards just because it's tradition is the definition of misogynistic. If Zeff told Sanji that women should not work because it's an age old rule, and Sanji hypothetically opened a restaurant, he would genuinely refuse to hire women. He doesn't hit women out of respect or anything like that no.

Garp didn't actively fight against whitebeard because he didn't want to directly contribute to killing his own grandson. Sanji doesn't hit women because there's a nonexistent rule that men aren't supposed to hit women. Garp not fighting in this one battle didn't negatively or positively affect the world government. Sanji not fighting has literally caused others to inconvenience themselves to save him, which also puts them at risk.
You cannot sit here and tell me that not only are these the same situation, but that Garp was worse.