Originally Posted by Zeful
The difference is though, you can take the sword away if it's causing trouble without inconveniencing the character for too terribly long. The spell by contrast cannot be so easily removed.
All this discussion of whether or not GMs should take PCs gear away and what the Gentleman's Agreement is or is not is missing an important point.
How does requiring a roll to learn a spell fix the problem?
If the wizard passes the roll then he's learned the problem spell and can't unlearn it any more that he could have without the problem spell.