Here's an easy way, ala Lion King
Let's say we become herbivorous - we start consuming plants. To fulfill our bodies' needs we need to consume a lot of plants. Now a lot of animals also eat plants, sometimes much moreso that we could. Now if we take away from their plate to fill our own, we essentially cause them to starve. If we don't tend to animals - thinning their numbers to curve over reproduction and thus have too many mouths to feed, we again are allowing them to kill themselves off. Predators exist to help keep the herbivorous population under control, killing indiscriminately but more times than not taking away females (since females typically outnumber males in the animal world). When they kill, they consume, because they cannot eat plants, at least not in good enough numbers and their bodies cannot break it down to use it. Humans were born to be omnivorous, meaning we need both plants and animals to be healthy, we just tend to go after animals more because of taste, ease of finding, and how it gives our bodies the sense of being full when we consume it. Plants (consumable ones) on the other hand, are not that easy to locate in the wild. You have to go to certain places to find food and even then, the fruits/vegetables/herbs we find do not hold all that we need to remain healthy.
Let's say we become herbivorous - we start consuming plants. To fulfill our bodies' needs we need to consume a lot of plants. Now a lot of animals also eat plants, sometimes much moreso that we could. Now if we take away from their plate to fill our own, we essentially cause them to starve. If we don't tend to animals - thinning their numbers to curve over reproduction and thus have too many mouths to feed, we again are allowing them to kill themselves off. Predators exist to help keep the herbivorous population under control, killing indiscriminately but more times than not taking away females (since females typically outnumber males in the animal world). When they kill, they consume, because they cannot eat plants, at least not in good enough numbers and their bodies cannot break it down to use it. Humans were born to be omnivorous, meaning we need both plants and animals to be healthy, we just tend to go after animals more because of taste, ease of finding, and how it gives our bodies the sense of being full when we consume it. Plants (consumable ones) on the other hand, are not that easy to locate in the wild. You have to go to certain places to find food and even then, the fruits/vegetables/herbs we find do not hold all that we need to remain healthy.