Hmm, the above comment somewhat implies that the reason why the RawTherapee devs have made it impossible for users to select an input class profile as the user-chosen output profile is to protect the user from making a choice that will lead to wrong results for users who don’t know what they are doing.
In my opinion, writing code specifically to protect users from making mistakes based on a developers’ opinions about what users do and don’t understand is a road down which developers of image editing programs should not go.
But I suspect that the real reason for leaving input class profiles out of the list of allowed profile classes for saving an image to disk is that the RawTherapee devs didn’t realize there might be workflow reasons for outputting an interpolated image file that’s still in the camera input color space.
I like RawTherapee quite a lot - it has some amazing editing algorithms not available in other image editors. But normally I don’t use RawTherapee for actually interpolating raw files, because of one specific issue with the RT processing pipeline - there is a bounded ICC profile conversion - possibly to LAB, possibly to the RGB working space, maybe through both of these color spaces, that clips out-of-gamut colors in the interpolated raw file (https://ninedegreesbelow.com/photography/linux-raw-processor-review.html#radiometric).
When I do use RawTherapee for interpolating a raw file, my workaround for avoiding clipped colors is to use an sRGB profile from disk as the input and output profile - thus avoiding any clipped colors from the RT processing pipeline - and then assign the camera input profile after opening the interpolated file with GIMP-2.9.
In other words, personally it doesn’t affect my raw processing workflow at all, regardless of whether RT does or doesn’t allow saving an image to disk in a user-chosen input class ICC profile.
However, if the real reason for making it impossible for users to choose an input class profile for the output profile is to protect users from doing something the RT devs think is not in the best interest of users who don’t know what they are doing, then perhaps a similar constraint should be put on the user’s ability to select a custom camera input profile from disk. After all, an sRGB profile from disk is not an “input class” profile. Rather it’s a “display class” profile.