If you put no fee, some big actors will create non optimize crawlers and call the service in a loop, wasting your tax money.
A small fee means people will take care of only get exactly the data they need, cache what they need to cache, and refresh only if they really need to, and what they really need to.
Otherwise, it's the tragedy of the common.
In Sweden most government data is public which includes individuals tax records.
That generates things such as news articles "The 50 people in your area that had the highest income last year" with home address and everything and that you can look up income instantly on the web.
Some level of privacy for this would be nice to have.