So how to change block size limit without using central authority ? Giving the power just to miners is easy solution but still miners dont represent whole Bitcoin economy. The ultimate freedoom would be if everyone could set in client how big blocks he considers valid (basically unlimited block limit proposal but for practical purpose everyone has to set limits), but this will cause a lot of chaos and put a lot of responsibility and risk to everyone how big block every individual has to set to have working client with most Bitcoiners (if he sets low value) - so the only safe solution in this scenario for everybody is set huge block limits (which dont matter if majority are small miners who make huge bocks invalid pretty quickly because before they download and confirm it most likely small block is found instead).