The 1 DEC listing fee was implemented by the Splinterlands company (I had nothing to do with it!) to prevent mass listings of 0.1 DEC rentals and constant rental price updates which caused their server costs to be too high.

Your take regarding the current proposal is correct, it is an additional cost to ownership that is realized when you sell. However, this cost isn't going to any person or company, it is going to the community (the DAO), which is controlled by you and everyone who stakes SPS.

In addition to funding the DAO, the main benefit of this in my opinion is that these DECs will no longer be circulating. What I mean by this is that I personally do not believe any proposal to spend/sell the DEC will pass until we are at peg, besides simply burning it.

With less DECs in circulation, there is less supply thus we get closer to reaching peg, which is ultimately the goal of this proposal.