what if someone makes writing error enough to search can't find a thread with the same subject?
Most of the duplicated threads come from the marketplace and altcoin discussion section, where the signature hunters post his shits. it's better to disable signature in this section, it would certainly have made a less number of double thread.
Writing error is exceptional case, I am suggesting a solution to avoid mistakes that majority of the users made here.
Signature ban in several sections is no doubt the best solution to restrict spammers but merit system made a lot of impact even without it.
We can't control spammers through this feature because it still depends on user that whether they are going to review suggested threads or they want to skip.