Not sure who those people are but not only is is inhumane to the prey but also increases danger for the snake, nothing worse than a stunned rat coming back from it's dazed.some people seem to think stunning a rat is a better option (which IS inhumane).
As far as feeding it comes down to a few thing first being knowledgeable and second being responsible (that includes, supervising, feeding a prey that is not too big etc)
Live is fine, F/T is fine to the question is which one works best for you and your animal.
Now as for the size keep in mind that BP in captivity are overfed and while they surely can take larger prey, larger is not better, none of my males eat prey larger than 55/75 grams, by doing so this allow the animal to feed with consistency versus having an animal that fast, I even skip a week here and there on a regular basis.