That depends on which humans and where. There are still plenty of tribes that live in areas where vegetation simply does not support their population. Luckily, humans evolved to be feed on more things than most things on the planet. We can eat plants, fungi, bugs, fish, etc.

So you're right. Humans don't need to kill animals. We can survive by killing just about any living thing on this planet. We can even eat things that would otherwise be super toxic to us by learning how to cook it, peel it, or skin it.