I always thought the "horde" was an interesting topic, because it's both what's good, and what's not good about a massive online game.
Here's the thing... the "horde" has a LOT of positives to offer, and as was previously stated, human nature tends to gravitate us towards that sort of thing. There's comraderie, there's a feeling of participating in something bigger than yourself, there's a feeling of accomplishment if the group you're part of establishes a CAP, sinks the carrier, or takes the base. There's a feeling of "belonging" and flying with a group of other like-minded people.
None of those have anything to do with score whoring, wanting to do overkill, or anything of the sort. The "horde" in my opinion is purely a function of social construct. It satisfies social desires, especially for people who are not known or well established in the game (which classifies probably 90% of the people out there). This tends to be the bread and butter of what keeps a LOT of MMO style games alive, INCLUDING Aces High. Doesn't matter if you're talking PvP or PvE.
As was mentioned before... at one time there used to be "anti-hordes" that'd up in defense, and would create some great fights. A lot of those anti-hordes no longer exist though. Why? What's the difference between then and now? A lot of people think it's the players, and yes, there's some change there, but a lot has to do with the game as well. Back in old Beta days, all you needed to capture an airfield was a goon and nerves of steel. You didn't need CAP, you didn't need to de-ack or take down a town. You just needed to grab a goon, drop 10 drunks on the runway (sometimes under the nose of the enemy), and the field was yours. Because it WAS so easy, multiple fields could change in a matter of minutes, not hours. Defense was incredibly important because if your country didn't participate in both offense AND defense, you'd find that you would be losing bases at a really rediculous rate, and not taking enemy ones nearly as fast.
In a strange way... the addition of difficulty to running bases has actually removed as much importance of keeping bases, and increased the desire for a co-ordinated (or just plain old horde) attacks as taking a base became far more important than keeping them. In old old days... the incentive for defending bases was because they were so easily captured, you needed to pay closer attention... now, there's not nearly as much incentive, and a lot of people figure with the radar, the flashing bases, the ack, the mutliple spawns, the town to take down... someone will eventually go over there to defend.. except there is no "someone" because EVERYONE figures "someone" will, and not do it themselves.
What's the fix? That's a tough one. The social aspect is not something you want to remove from the game because it's the exact same thing that helps keep it alive. Incentivize defense in some way? Perhaps that would help. Make base taking easier? Who knows. Lots of talk about making it tougher over the years is why we are where we are now. Is it even something that NEEDS to be fixed? Well that's the real question in my opinion, and even to that, I could see arguments for both sides, and frankly have no idea what the "right" answer is, other than if I were in HTC's shoes, I'd do whatever answer keeps him running the longest (which is, I'm sure, what he tries to do).