This is so ridiculous. "Hitting on" someone is an attempt to find out if the attention is wanted. It can obviously be done in very poor taste, to the point of being abhorrent, but it can also be done respectfully. To say that he was wrong to hit on her because it was unwanted attention is completely circular logic.I did not saying that hitting on women is always wrong. I indicated that walking up, rudely interrupting someone who is talking to someone else, and then presenting weird and likely propositions to her is NOT OK. In your words, this is hitting on a woman "in very poor taste, to the point of being abhorrent."
Serious question: in your version of the ideal world, how does anyone ever begin a romantic relationship?
Seriously? Here is a strategy for hitting on women in a respectful way.
Step 1, do not simply barge in on a conversation, find someone who seems open to conversation and engage politely. Sometimes this is as simple as listening to a conversation for a bit then interjecting. Sometimes you see someone standing there who seems bored. Sometimes you need to sit at a random table and start talking with people around you. Sometimes you're both in line for something and you make a remark to the person behind you.
Step 2, engage in neutral conversation. There is a ton of stuff you can talk about. If nothing else you're at a technical conference. You can ask what the other person does, how they are enjoying the conference, etc. Don't forget to use your ears - people like to be listened to.
Step 3, assess the possibility of interest. There are a number of socially acceptable ways of doing this. One is to tell an off-color joke. Another is to point out someone else who seems to be headed towards more intimate behavior. Or you could make a mildly flirtatious remark. If a woman is happily interacting with you, and responds to a sexualized twist in the conversation with increased interest, there is a possibility that she could become interested in you. If she is draws away from that direction, that's a sign that she is not interested. But you can go back to step 2, and wind up having had a good conversation.
Step 4, if more charged topics have come up and are acceptable, then you can make your pass. Even if you're turned down at that point, she shouldn't be offended.
Note that at every step along this way you can break off and have had a mutually pleasant interaction. If you don't think that this is true, you should be talking to someone else. While getting laid might be a welcome surprise, that isn't what you are there for.