This alleged conspiracy would involve
(a) some rather rapid negotiations for a sum that wouldn't be much below the market value of Twitter,
(b) the believe that now, 24h+ after it broke on Twitter, it has not made the jump to many other distribution channels already, and
(c) the complete idiocy of United and Twitter in thinking such a scheme would not be noticed or, if noticed, would not result in coverage orders-of-magnitudes worse than what they deleted. Oh, and
(d) apparently they forgot to delete the original tweets, which were the one actually being shared.
All that is quite implausible, even though it may be possible. Here's an alternative theory: Twitter has, in an attempt to combat spam, implemented a filter that registers a sudden rise in certain keywords, maybe within a negative context. Once triggered, it throttles new tweets that match automatically, until someone overrides it manually. This system just failed spectacularly, because it had never before seen such an amount of tweets with such an imbalance of sentiment.
I'm not saying that the latter theory is true. I just believe it's much more plausible than Twitter just throwing its business away. And while I don't care much about this specific company, I believe something larger is amiss when every single event is always interpreted in the worst (barely) possible way.
If everyone and everything is assumed to be corrupt, pretty soon that's how it's going to be–either because it doesn't make a difference for the pitchfork-people if I'm really corrupt (or just incompetent/unlucky) so why bother? Or because those with pitchforks don't see problem with becoming corrupted themselves. Everyone is doing it, after all.
So, in an attempt to stem the tide of corruption, people scream for transparency, and everyone is accused, everyone is a subject, everyone is under investigation. That, however, cannot work: a liberal democracy does not have the means to audit and control everyone. A free society, and an advanced economy, is sustained by 98%+ doing the right thing even when nobody is looking. That, and the trust it brings, and the institutions it makes possible, is basically the difference between Canada and Somalia.
So I'll delay my scorn for a day and see what Twitter has to offer, and I'll needle the guy I know there with jokes and watch him turn red, and I'll know that moment of shame is (for him) more of an incentive to do better than a million hateful tweets would ever be.