As long as a user can only run the code they (or the page author) has entered by themself, I don't see an issue. It gets more problematic if you allow users to

As long as a user can only run the code they (or the page author) has entered by themself, I don't see an issue. It gets more problematic if you allow users to store modified cells and link to them. Then a malicious user could write a cell amd trick another user into executing it.