It's been discussed thoroughly, and I won't need to wander far to find supporters for the point... Jails don't work.
If a player can shrug off a ban, and not learn from it, it's likely they can shrug off a permanent ban
Also - I believe a month is a very severe ban. Anything within this range is appropriate in comparison with how heinous the act was.
Anything more, and other actions (permenant) should be taken into consideration. Also, I find pillorying people for more than 20 minutes doesn't seem to work either.