I completely agree with both parts of this quote. The tongue is sharp and satirical. The words which roll off the tongue are capable of killing...they are, can be, and have proven historically to be deadly. The tongue is also blunt in that it is not pointed as a sword would be, but it is brutally honest and forthcoming. So, "the pen is mightier than the sword" takes on a clearer meaning...if the tongue delivered those written words, it would also be sharper, deadlier, and perhaps more blunt than the proverbial sword.
Perhaps there is a double entendre upon the words "blunt instrument." For, to be blunt is to be brutally candid--an action which can certainly damage the sensibilities of people. For example, the cruel cyberbullying of some has been responsible for the deaths of vulnerable, sensitive people.
With this meaning of blunt, therefore, the quote is much like the oft-cited, "The pen is mightier than the sword." That words, be they spoken or written, carry a power is evident throughout history. Was not a presidential election significantly determined by the word change? How many people cite what they have been told by TV jounalists, evangelists, etc. as dogma?
Indeed, the tongue is deadly when a cult or fanatical religious or political leader speaks to his following. For, the people's attitude is set by the words of this leader, and action is spawned from the words of radicalism, action that can be dangerous and deadly. History is replete with examples from the Puritans to the Nazis to the Al-Qaeda.
I agree with half of this quote, but not with the other half.
I think there are two parts to this quote. One says that the tongue is deadly. The other says that it is a blunt instrument. The first part is true, the second is not.
When we talk about blunt instruments, we mean things like sledgehammers -- things that crush what they hit but cannot be used with any finesse or precision. This is clearly not true of a tongue.
Because tongues are not blunt instruments, they are dangerous. People who are skilled at speaking can cause all kinds of problems. They can destroy another person's reputation or they can persuade the people of a country to do something that is really not in their best interests.
People can say the most cruelest things in the way of speech vis-a-vis rumors, gossip, etc., and this can be very hurtful and painful for people to hear. Also people can lie about things and cause an unbelievable amount of damage from it.
The feeling of pain and hurt that are caused by unkind words are worse than the pain of physical hurt. Besides wounds of hurt feelings take much longer to heal than physical wounds. In this way the physically soft and blunt tongue, as an instrument of speech, is capable of inflicting much deeper psychological wound, than the deepest physical wounds that can be inflicted by sharpest of instruments. The harm done to the peace and happiness to this world by tongues is perhaps much more than the harm done by weapons of war. because the speaker who inflicts the wounds is not aware of the damage he is doing to the listener.