[indubitable]

In my opinion the upvote system gained popularity not as anything like an effective means of content ordering (even if that was its original intent) but because it's an effective means of site growth. It turns discussion into a game where you can get, or lose, points and creates an emotional response system not all that dissimilar to the blinking lights of a slot machine.

An interesting thought experiment. Imagine a site like Reddit disabled all external numeric displays of score for a year. You'd only have indirect indicators like order prioritization and apparent visibility based on the number of comments responding to a post. Would usage increase or decrease relative to what it would have otherwise? In my opinion it would not only decrease, but somewhat precipitously. There are a vast number of people that seem to participate almost solely as a means of increasing their score. And even for those not fully addicted to the system, it certainly provides an emotional feedback mechanism. Without this, I do not see these users participating as much - nor do I see a sudden influx of others to replace them. On the other hand, I also imagine this would likely substantially increase overall quality. Like you mention low effort content that incites a reaction is a hallmark of gaming these score systems.