I understand where you are coming from. I've seen one too many times where the guy has been "dissed" after having cold turkey approached some woman. I think they act like this for various reasons. Reasons that I can "see" as a woman myself. For one, women are suspicious sometimes when men approach her like that. She doesn't really think they're serious. Also, she may be happily involved and go on the defensive if you talk to her out of the blue. Especially if she doesn't find you attractive. In her mind, she's thinking, 'What the hell are you talking to me for?'
Lastly, and this is a big one for me personally, is that she's kind of shy. A woman will send "false negative" vibes to men she finds irrisistibly attractive and want to get with. She's just acting in a nervous way, because she's happy and can't believe that you've actually spoken to her and shown some interest.
In this day and age, I wouldn't approach people like that unless you don't mind getting rejected. I would gradually try to talk with women I already know, like co workers, or acquaintances. You have a much better chance at finding someone through those type of people than strangers on the street.