You can feed live, but there are risks involved, especially to the eyes and face of your snake from a prey item that is fighting back. Also, there is a big risk if your snake doesn't eat right away, a larger mouse(sub-adult or larger) will actually chase your snake and bite through it's skin. Obviously, if your snake is locked in a feeding tub with a live mouse, and doesn't eat right away, it can't escape if the mouse gets bitey.
If you must feed live, please be sure to stun your prey first with a quick thump on the head or against the edge of a table to immobilize it and prevent any injury to your snake.
But...like LennyCorn said...if it ain't broke, don't fix it. I have an MBK that I am desperately trying to break of the live habit. I WISH she would take f/t, but she will only take live. Consider yourself blessed if your snake takes f/t.