To me the word "legitimate" is the main problem.
Who can claim the power to say: this data is legitimate and that another is not legitimate. This is called censorship!

The question can not be: What data is legitimate to be stored in the blockchain?
Because this is a subjective question, and that no one can claim to have the answer.

The only question is: Should we allow the storage of data in the blockchain?
And the answer is: there is no choice, because it is possible to do with multisig transaction.
So the question becomes: Should we let people store data in multisig transactions or provide a cleaner way to do it?

History has shown that it is much smarter to regulate than to ban something that is impossible to ban.