Banning someone, means that someone is being removed from the community. Theymos wants to remove someone from the bitcointalk community, only as a last resort, even for people who cause problems for theymos personally.
Which is why I suggested escalating levels of temp bans first. If you've been temp banned four times already for spamming, and are still continuing to spam, then you are never going to change and banning you permanently is a suitable "last resort". Exceptions can be made as they are with the plagiarism rule for less black-and-white cases.
All you need is someone to start locking up threads so that you don't get waves of redundancy.
I don't disagree that spam/repetitive/redundant threads need locked, but this does not address the underlying cause of the problem. There are always more threads to post in and spammers can also open new threads faster than they can be reported and locked. Spammers chasing a paycheck will always find a way to reach their quota, whether or not 90% of threads are locked. It will just make the unlocked threads even more unbearable. The only solution is to starting handing out real punishments to the spammers and the campaigns which encourage them.