I thought "lady" was analogous to "gentleman," is it really patronizing? I've always used both of those terms when I'm trying to be more polite or formal than usual.
So I'm curious as well but I know many female friends who prefer to be called a lady / ladies so I'm not sure you can necessarily win when you attempt to converse with someone and you have zero context about them.
I think people need to be more forgiving with most labels when the conversation happens anonymously without context of that user's preference. Now if you referred to them as "bitches" that would be a problem but I feel like we can be forgiving for "ladies", even if a majority of women do not like it.
Nothing. It is a term generally used out of respect or formality like gentleman or Lord. Though I guess there are usages where it is just a gendered pronoun.
The only context I've seen where 'lady' might be offensive is when some men enter a room full of other men and addresses them like "hello ladies".