The main difference between the two communities is the ratio between what I'll call the 'experts' and the 'fools'.
'Experts' are people who have a solid background in the topic they're discussing. When it comes to technology, these are often people who have one or more degrees in fields like math, science and engineering, in addition to other more specific training. They have years of experience in industry working on real systems, or working in advanced research labs. They know what they're talking about. When they post a comment, it has real, intrinsic value.
'Fools' are the opposite. They have limited, if even any, relevant education or practical experience. In many cases, they're so ignorant that they're completely ignorant of the fact that they're ignorant. Thus each and every comment they make is full of nonsense.
So here at HN, there are a very small number of 'fools' for every 'expert'. That's why the quality of discussion here is generally so much higher. There's real insight in the discussion here, because so many 'experts' are involved.
It's a different situation at /r/programming. For every 'expert', there are literally thousands of 'fools'. Any relevant discussion from 'experts' is drowned out by the sheer volume of junk from 'fools'. Worse, the 'experts' often have their comments down-voted, which essentially removes any trace of intelligent discussion. All that remains is stupidity.
I don't think that people here necessarily hate /r/programming or its users. It's just that many here likely see it as a waste of time to deal with that community, and with the ignorance that permeates it. And it's hard to take them seriously because of the low-quality discussion that often happens there.