As our community has grown in numbers and in breadth, the number of accepted papers in STOC and FOCS has stayed the same. This is causing more competition for acceptance, with the usual consequences: "safer" choice by the committee, a feedback effect on the community, making people focus on the more popular topic, general unhappiness, some subcommunities splitting off to their own specialized conference, and so on. The change that you propose would effectively kill off STOC as a "prestigious" venue, and so we would double the pressure on FOCS. I could imagine that junior people would send their good papers to STOC, hoping that, despite the five parallel sessions, many people would come to the talk, but then send it again to FOCS, in order to have the "stamp of approval" of a selective conference in their CV. The net effect is that the competitiveness and general unhappiness will only get worse. I also have one general and one concrete objection to big conferences, such as this new hypothetical STOC. The big conferences like the International Congress of Mathematician, or the Modern Language Association Convention are products of times when travel was difficult and expensive, but it was necessary because conferences were the only ways to see new work. So it made sense to have a conference that everybody would want to go to, but just one. Now we have various ways to stay in touch and to obtain papers without going to a conference, and travel is still hard but it is not so bad to go to two or three conferences every year. So it makes more sense to have relatively smaller events where the quality of the interaction with the other participants (the main reason to go) is high. When we have a very big conference, involving four or more parallel sessions and five hundred or more participants, the conference cannot be held in a normal hotel, which does not have the necessary facilities, so it has to be in a place that specializes in large conventions, which is more expensive, and is often located in unattractive locations. Eveyrthing becomes more complicated, from having lunch to finding the people you want to talk to. Instead of going in this direction of radical change, which could bring several unintended adverse consequence, I think we might instead trying to gently increase the number of accepted papers at STOC and FOCS, and to find ways (for example, co-locating other conferences) to increase participation.