Valid - but for what it's worth, I get a lot of real connection out of them. And I've never raced toward anyone just because they're successful, and I accepted every meeting request. 

Serendipity is good, but it would be very strange if trying to aim for conversations you like didn't improve the resulting conversations.

Don't underestimate the loss of being stuck in conversations for longer than you wanted. There are a lot of personalities who benefit from a time limit. 

I strongly disagree with the sentiment that 1-1s are dehumanizing, as I have found that most of my 1-1s have been friendly, warm, and fun even though they were mostly confined to 30 min.

Something else I can recommend is taking a walk around the block with someone instead of sitting at a table facing each other. This makes it more casual and less formal.

Overall I understand your idea that 1-1s can seem too business-like but my impression is that there are a few tricks to approach them in a way that is more fun.

Regarding your example of meeting the best people in the strangest places, I also make sure to add randomness to my conferences: https://forum.effectivealtruism.org/posts/ixdejJKnonBmaiF4T/add-randomness-to-your-ea-conferences

I think 1-on-1s have their uses, but at the EA conferences I went to this Spring, I did find myself  wishing that there was more space for unstructured group conversations (e.g., possibly physical spaces where you could go and sit if you were open to conversations with strangers). 1-on-1s can be very intense, and since my aims were somewhat vague, I think I could have gotten value out of meeting and chatting to more people casually.

Like others, I empathise (quite a lot, for reasons stated by Amber) with the gist of this post, but have met a lot of interesting people in (planned) 1-1s. 

I'll just point out one specific point: 

You could be getting into a wonderful conversation -- but then they have to go. "Sorry, I'm meeting someone else in ten minutes".

I think this is a good and prosocial thing to do, and doesn't dehumanize but instead shows respect for the other conference attendees you have meetings with.