As far as I remember, the main difference in point of view was that the PNG guys (rightly so, IMO) saw animations as something different from a still image, and wanted to keep that distinction, also in the face of MIME types, file headers, file name extensions, etc., while lots of other (misguided) people wanted animation as a feature in an image format, because they were used to that from GIF.

There may have been some bad blood from MNG, but that was not the main point as far as I understand. Although I must say that the links you provide are interesting reading.