Form over function, as usual.
- No gigabit ethernet
- No FireWire
- No built-in optical drive
- Only one (and bad) USB port
- No card reader
- No ExpressCard slot
Samsung X360 is way better hardware.
Consider that there are some people who need none of the things in this list and are able to do their work without them quite nicely. For over 4 years I led the development of a large software application (hundreds of thousands of lines of C++) that performs at enterprise levels (hundreds of millions of txns per hour) on a Windows laptop with lower specs than the 1.8GHz MBA (and much worse battery life). I had no difficulties whatsoever, never missed any of the items in the list above. For me, the MBA would be a performance upgrade in every respect. It's not relevant that there are other, more powerful computers out there...sure there are...but I don't need them.
Now, within that group of people, there are people who have enough disposable assets that the price of the MBA is not a significant purchase. From personal experience, I know that ticks some people off. I wish that wasn't true, and I don't think that having extra cash puts any of those people into any kind of "oooh we're special" category...but I don't think it deserves other people's disdain.
Finally, within that group of people, there are those that would much rather have OSX than Windows...thereby totally disqualifying any of the "I'd rather have a Samsung/Sony/Dell/ASUS" considerations. In that sense, they can't match the MBA specs...after all, software is a part of the laptop as much as hardware is. And, some of those people just like how the MBA looks (same way they like how a Tesla roadster or a Merc or a Lexus looks).
For that group of people, the MBA could be a nice fit. You might call those a "niche market"
Now, to the question posed by the OP: Why do people who aren't in that niche hate the MBA? For some people, it's just that they can't identify with anyone who doesn't want the absolute most power for the least money they can spend, regardless of whether they need the power, and regardless of how the cheaper laptop works (e.g. is it heavier, does it run Windows vs. OSX, etc). That doesn't make those "non-niche" people bad--it just means that they don't understand the other person's point of view.
For others, it's a matter of not agreeing with the idea of buying something because it looks nice. I'm not talking about buying something *just* because it looks nice. I mean, it has to meet my functional requirements first, but within that constraint, I'd like to buy something that I think looks nice. For some of those people, they think that's the same thing as buying it *just* because it looks nice, and therefore they look at the "niche" person with contempt. Again, that doesn't make the "non-niche" person bad, it just means that they think that a person that values form may not always make sure there's sufficient function (in the purchaser's eyes) to go with it. Sadly, the real world does give them plenty of evidence to believe that's true!
And, finally...to be honest, it just makes some people unhappy that there are things that other people can afford that they can't. That's an unfortunate spot to be in, and it's going to be a source of unhappiness for those people for a lot of things, not just the MBA. There are plenty of people who can afford things I can't, and there are people who can't afford things that I can. If you measure your happiness against those standards, you can't ever win.
Lots of philosophical BS here, but the main thing it boils down to is that there are people who think you're stupid if you don't think the same way they do.