Sitting around waiting for his nuts to drop doesn't make too much sense either.
People don't suddenly become brave as they grow older. The reverse is more often true; experience teaches youth they are not immortal and their willingness to court death wanes.
I will grant it may be remotely possible that the man would eventually decide to go on a killing spree, but locking him up for talk is wrong on so many levels I don't know where to start.
Before the "Kill all dem towel-heads" crowd screams "Soft on Islam consider that we have a thread devoted to a case of a man reported as killing his own daughter. An action, not words. See my response there before you embarrass yourselves. If such a thing is possible.