What if Zimmerman had a taser....and Martin had a gun. That would not have been a good ending for Zimmerman.
What if the Founding Fathers had only had sticks and stones?
What if, what if, what if......
There are Taser models that offer multi-shot capability ('X2' model) and those which can be used as contact Tasers in the event the shot misses.
In self-defense training with firearms, a good instructor will teach students that there's a 21-foot distance where use of deadly force is prescribed because handgun bullets -- like medicine -- often need time to take effect. An assailant armed with a knife can take several shots to critical organs, cover the distance of 21 feet in an eyeblink, and still carve up a pistol-armed defender like a Thanksgiving turkey before finally expiring -- even if he's still getting shot repeatedly.
In that situation, a Taser is actually more effective than a pistol-caliber handgun. You get a solid hit with a Taser, and you're going to the ground for awhile unable to do very much except make little squeaking noises. Comparatively, a pistol shot must strike a vital organ or the nervous system to achieve a 'stop' on a hostile target, whereas a solid Taser hit can pretty much end the fight right there from a pretty long distance distance even if the Taser projectile strikes the subject an area where a handgun bullet wouldn't achieve any suitable effect.
They're two different defensive means that only share some similarities.
Now if you want to continue to play 'What If?', maybe we ought to wait for an ancient Spartan hoplite to come in here and post that the nine foot long bronze spear beats absolutely every other weapon in the world at short distance when properly employed.