The goal of the GPL was to protect the 4 freedoms. Every change that the FSF made in the GPL 3.0 was because industry came up with new practices to subvert the 4 freedoms in some way, so it was necessary to update the license. When you add the “or later” to the license, you have a way to prevent the next way that the industry attempts to subvert the 4 freedoms.
I trust the FSF to be a good steward of the license more than I trust the software industry, because history shows that it will think up ways to try to get around the license.