Proposals for making LW upvote-only emerge every few months, most recently during the retributive downvoting fiasco. I said then, and I continue to believe now, that it's a terrible idea.

JMIV is right to say in the ancestor that subtle features of moderation mechanics have outsized effects on community culture; I even agree with him that Eliezer voiced an unrealistically rosy view of the downvote in "Well-Kept Gardens". But upvote-only systems have their own pitfalls, and quite severe ones. The reasons behind them are somewhat complex, but boil down to bad incentives.

Imagine posting as a game scored in utility. Upvotes gain you utility; downvotes lose you it; and for most people being downvoted costs you more than being upvoted gains you, though the exact ratio varies from person to person. You want to maximize your utility, and you have a finite amount of time to spend on it. If you spend that time researching new content to post, your output is low but it's very rarely downvoted. Debate takes a moderate amount of time; votes on debate are less reliable, especially if you're arguing for something like neoreaction or radical feminism or your own crackpot views on time and dimension, but you're all but guaranteed upvotes from people that agree with you. Plus telling people they're wrong is fun, so you get some bonus utility. Finally, you can post cat pictures, which takes almost no time, will score a few upvotes from people that like looking at their little jellybean toes, but violates content norms.

Which one of these is optimal changes, depending on how tolerant you are of downvoting and how good you are at dodging it. But while removing the downvote option incentivizes all three (which is why social media likes it), it should be clear that it incentivizes the last two much more. You can see the fruits of this on Facebook groups, that site's closest analogy to what's being proposed here. (Tumblr, and Facebook user pages, are also upvote-only in practice, but their sharing and friending mechanisms make them harder to analyze in these terms.)