Something I've tried to explain to our clients (and our sales people) in my job is that the existence of outliers on a curve of possibilities does not invalidate the mean. Just because it's possible for some odd thing to happen now and then doesn't mean that it will happen regularly.
But I guess it's human nature. I've been reading Christian Wolmar's book On the Wrong Track: How Ideology and Incompetence Wrecked Britain's Railways, which, among other things, blames some horrific railway accidents on the way in which the British railway system was privatized. I bet that a lot of people in Britain think rail is the most dangerous way to travel, when in fact it is among the safest. People assume the outliers are the mean.
Meanwhile, the scenario where a horde of people take advantage of these $20 Worldcon memberships to flood the Business Meeting and vote themselves a bunch of Hugo Awards is just silly. On top of the fact that there's no way enough people could be rounded up to try it in the first place, there are so many procedural safeguards1 built into the system to prevent "meeting packing" that it's just ludicrous that people would think it's even a possibility in the first place.
1Taster memberships can be used once per person, so you can only flood the meeting on one day. But the WSFS Business Meeting takes place over (usually) three days. You'd have to get enough people to show up on day 1 to avoid having your motion squashed by Objection to Consideration. Then on day 2, you'd have to flood the meeting again to actually pass it. But wait, you're not finished yet. Any canny BM regular, realizing that the meeting was flooded with one-shot attendees would vote on their side; then, on day 3, they'd vote to reconsider the early vote on passing the motion. This means you'd have to either flood the meeting a third day, or try what is known as "spiking" reconsideration; but there is a counter to a "spike" designed for such scenarios (it's called "Reconsider and Enter on the Minutes") and in such a wild situation, I expect it would be used.
But let's say you get by all those hurdles and your proposal has passed. How are you going to transport all these presumed Business Meeting Zombies to Japan to get your proposal ratified next year? The 2007 BM would reject ratification, and all your efforts (not to mention all the money you spent to buy memberships for the zombies) would have been in vain.