I know that some women find this behaviour insulting. That they are annoyed by it if some creepy older man starts calling them 'sweetheart' but you have to look at it in context to justify calling such a phrase a form of harassment. Had said man followed said woman out of a bar and then called her 'darling' that would be creepy and definitely be harassment. Had he tried to chat said woman up inside the bar the same interpretation would apply. However, what if this man was just the bar man and said it to all of his customers just as a small part of his friendly disposition? Of course the woman has every right to find this irritating, we're all different, but there's no way it can be labelled as harrassment. And sometimes it is. Or at least complained about in a manner that would suggest it was some awful sexist faux pas.
It's terribly precarious territory to start accusing women of making a fuss over nothing and I am by no means trying to make such a point. That's why we have such shocking stories of rape being unabashadely ignored. But if you start throwing accusations around of every day politeness being yet another form of sexism then we get ourselves into another mess.
If as a woman, or even as a man, you are offended by being called certain names such as 'darling' then make sure that if you show coldness to whoever said it because of this that they weren't just being friendly. We need more friends in this world as it is.