I think that the default options should be set with the new(er) to intermediate users in mind. Those have certain expectations, real or not, and are used to OOC images and what they initially see on the back-screens of the camera. Seeing a RAW image in darkroom view that looks (half) decent is a good starting point for them.
Once you are familiar enough with darktable and know how to unleash its power you can easily set the preferences to your own liking.
Although I try to convince people to use the linear rgb way of working, I don’t think it is a good idea to push them, which you would probably be doing if you turn the base curve off.
As already mentioned by @anon41087856: If you turn off the default base curve it does need to be replaced. But with what? And based on what?