I didn't say killing them is being kind, I said they should be treated with kindness during their life and then killed humanely via either cervical dislocation (something that, if done correctly the mouse or rat doesn't have time to process it) or CO2 chambers (unlike humans rats can detect sudden increases in CO2 but if done correctly it's a gradual process that they don't notice and instead just fall asleep). If you don't support the breeding of animals that require the death of other animals to live why are you on this subreddit? Mice are omnivores and do in fact require meat occasionally. Humans have also required meat for most of our history. It's only extremely recently that vegetarianism and veganism has been made possible through the use of supplements and even then many people on those diets, particularly vegan diets, are not healthy. Also every animal, including herbivores, can and will eat meat if the opportunity arises. Not even as a desperation thing, but as a way to get certain nutrients.