I'm not sure why it would be too hard to objectively say when a question should be tagged rationale.
If a question is about why something is practiced by a travel-related entity, then it's a rationale question.
Why are airlines against the transferring of tickets to other persons?
is a rationale question. But:
Can I transfer my British Airways ticket to another person?
should not be tagged with rationale.
I don't see how this would be too subjective? I think the definition is quite straight forward? Maybe you could give a few examples of questions that are in a sort of gray-area between being suitable for rationale and not being suitable? I'm open to having my view changed.
Awaiting further discussion, though, I'm going to say it's pretty straight forward to know which questions to tag with rationale, and I think we have a pretty objective definition for it (as described above.)
- We have an objective definition for the tag (I believe we do.)
- We think such questions are on topic (I think they are.)
- The tag helps distinguish such questions as a group (I think it does.)
Then I don't see any reason to get rid of the tag. It seems useful to me.