I don't think reacting to something because you've been conditioned to it during your childhood necessarily reflect your beliefs as an adult (maybe that's the point where we fundamentally disagree)
We indeed disagree on this point.
In my opinion, it does not matter "why" Sanji is the way he is. I see it as little more than trivia. Most of any adult's actions or beliefs can be explained if we look at their childhood, but said childhood only serves to explain "why" said adult is the way he is, it doesn't serve to excuse what an adult does. Sanji simply is the way he is.
The kind of gentlemen that believe they should always pay in a date and all of that are sexist. Sexism isn't only about being rapists or beating up girlfriends. Sanji is an extreme trope of that kind of gentlemen, which makes him inherently the most sexist character on the crew.
Anyone who will refuse to hit a woman under any kind of circumstances simply because they're women, is sexist. Treating an opponent differently in the same exact situation based only on gender is by definition sexist. Is it the fault of the education he got? Maybe, but that doesn't mean he is not the way he is. In his case, it's pretty extreme since, as you say, he can't even use hardening to block Black Maria (yet he somehow used black armament and even diable jambe immediately to stop Big Mom's punch despite the risk of burning her (which should be painful even if it doesn't "injure" her, like Law's counter shock). It does seem like he's more of a "gentleman" the more beautiful his opponent is). This to me only seems like the sexism he exhibits is very deeply rooted.
Which is why, even though Zoro is pretty sexist (Zoro is kinda like most adults from before the 2000s), I see him as clearly less sexist by comparison. Does he "belittle" women by not fighting them all out? Yes, though this has only been seen so far in the Monet fight in more than 1000 chapters. He didn't fight Tashigi seriously because he didn't even need to do it to defeat her and because she reminded him of Kuina. Other than those two fights he's taken care of swiftly of any female opponent he has encountered.
And even in the Monet fight, the only fight in which he has seriously come out as sexist, he found a way to fight and defeat her. This means that while he may have "belittled" her by not going all out, at least he was capable of considering her an opponent and an enemy. Zoro didn't use CoC on Monet. Zoro slashed Monet's cheek to make her feel:
1- That Zoro could injure her with CoA despite her being a logia.
2- That he could cut up a woman, which he highlighted by his dialogue about being a caged tiger.
Then he just showcased his superior speed and strength to make her scared for her life and faked a cut in which he didn't use CoA but showed her she would have been cleaved in two if he had. Monet didn't faint like CoC victims do: she was so scared for her life she lost her mind and had an anxiety attack.