Because if your never going to be able to use you powers in a way that is dependably safe, why should you have to pay for them?
"Because you don't put a bomb on stage unless you plan to have an explosion." That is a quote from an interview about Angels and Demons (the film). So why should anyone want to play a Loup-Garou if they will never let their beast run wild?
But the fact is, that such a character is definitely evil (or just psychotic) if the he or she doesn't have an attitude of "I can't be allowed out during my time of the month." For only a horrible (or insane) person would risk the safety of innocent people by being out near the full moon.
So basically your character is missing anytime the full moon is up. And what is the point of playing a Loup-Garou character unless it will come up.
I would allow a Loup-Garou PC to be controlled by the player, but there would be compels to pursue the rage. If there is an enemy around (and the guy was conscious of that before turning) I would allow target priority, but otherwise, they try to rip apart whatever is close (or noisy).
And I think a character like this is really interesting. Trying to balance a normal life while being cursed could lead to some fun role play.
"Interesting" isn't the same as "Playable."
Loup-Garou PCs (like "evil PCs") are "interesting" to play but annoying as hell to everyone else.
There are many other ways to play a "tortured" (emo) characters in DFrpg: Red Court Infected, White Court Vampires, Emissaries of Power, and even Changelings (to name a few). And none of them are time bombs (well I guess Red Court Infected could be... but if they slip they are either an NPC or killed off anyway).
But it doesn't matter, by the rules as written, a Loup-Garou is a -21 refresh character. At 21 refresh, I think the rest of the party can restraint the character if necessary.
Figure a Superb Might for an effective Legendary + 5 (13) Might for Lifting and
Breaking. I think a -21 Refresh Wizard can throw up an 18 shift block with Thaumaturgy (might need more though to protect against fate points).