The Culture is an anarchic democracy: if all but one single GSV had voted to disband, or to become a dictatorship, that lone GSV could disappear elsewhere without anyone stopping them.

They were up for, and welcoming of, even quite extreme changes; compare with humanity today, where being transgender is considered controversial by a significant percentage of the population of a nation that likes to self-promote on the idea it is the beacon of liberty and freedom, versus the way Culture bodies are written to be able to flip gender more completely than our best biotech and just by conscious will, with most people being expected to try it, and with some couples flipping gender while pregnant and pausing the pregnancy just so both can give birth together.

Even species changes are, for them, easy and of no great consequence or dispute. While you may be seen as weird if you choose to give up the visual accuity of an owl and the cerebral resliliance to survive decapitation in order to live out your life on this quaint rock recently discovered to be hosting an atomic age civilization, the Mind won't refuse to change you into a mere human just because you found Jesus.