Vegan reply to: “If we left nature alone, there would be millions more wild animals killing humans!”

You wrote: “No I don't think it's morally justified as I don't believe in killing a fellow human.”

Okay in order not to be speciecist, i.e. in order to not discriminate based on species, you have to include animals in your moral concern.

“Speciesism and human slavery are similar in that in all cases animals and enslaved humans have a basic interest in not being treated as things and yet are treated as things on the basis of morally irrelevant criteria. To deny animals this basic right simply because they are animals is like saying that we should not abolish race-based slavery because of the perceived inferiority of the slaves’ race. The argument used to support slavery and the argument used to support animal exploitation are structurally similar: we exclude beings with interests from the moral community because there is some supposed difference between ‘them’ and ‘us’ that has nothing to do with the inclusion of these beings in the moral community. The animals rights position maintains that if we believe that animals have moral significance, the principle of equal consideration requires that we stop treating them as things.” – Gary Francione

In order to not be speciecist, you have to include them in your moral concern and not to kill your fellow non-human animals for food, clothing or any other reason.

“If we left nature alone, there would be millions more wild animals killing each other and millions of animals like wild cats killing humans!”

First of all your argument is not related to the reason why people domesticate, enslave and exploit almost 60 billion land animals per year for food, and exploit more than 1000 billion marine animals per year; neither the driving force of why people are hunting. The driving force behind all this is the viewing of animal as commodities, and killing/hunting and eating for pleasure, taste, convenience, habit or tradition.

You are assuming that there would be million predators killing humans.
There is a nonviolent solution. We could live in ways to protect ourselves from wild cats and other predators. You are trying morally to justify violence to prevent other sentient beings potential violence against humans. Would you ever believe it is justified to kill another human just because you saw him/her as a potential threat?

I am opposed to violence. I recommend this article: http://www.abolitionistapproach.com/a-comment-on-violence/#.UaCzxZxc18E