The "humane" argument is flawed because in the end - factory or pasture - the animal is killed. Live a happy life and be slaughtered or a miserable life and be slaughtered.
Pure conjecture. All numbers I've seen show a higher quantity of deaths from crop farming per calorie.
Additionally, the crops where some of the highest number of field deaths are encountered (such as soy and corn) are also primarily as animal feed.
So no. Vegans do not kill more animals.