The human race deserves to exist simply because we evolved to this stage of our development. As humans evolve our thinking, eventually we will solve problems of poverty, disease, prejudice and violence. We deserve to exist because we are capable of learning to better ourselves. Those who adapt well enough will survive, just like Darwin's survival of the fittest theory.
I would have to say that this is really broad question whether if deserve to exist. I believe that if we are allready here then we deserve to exist. I mean every creature on the earth has its destiny. If we are allready here then I guess god has made that choice for us.
In order to answer this, one first must address the term "deserve." Inherently, the term implies that there is some obligation of another party to uphold a social contract to the first party-in this case, the first party would be "we," which I will assume is meant to be humans, but the argument is applicable to a broader or more specific spectrum, as well. The problem, however, lies in both the origin of the obligation-the social contract-and the nature of the other party. By what rules are the social contract bound, what are the consequences of breaking it, and with whom is it made? There are theories of one or more deities who simply claim that humans "deserve" to exist, but these serve no logical basis to advance any such claim, and in fact inhibit it due to the wildly increased presence of logical stress. Moreover, unless the rules and consequences of any such contract can be clearly defined in order to establish whether or not any breach of such contract has occurred, any claim regarding that humans deserve to exist can only be deemed pure speculation at best. And, without proof or even reasonable evidence that humans do indeed-inherently, or more likely but still remotely by some social contract-deserve to exist, then regardless of the actual existence of the species, the claim that we deserve such simply stands as speculation and, dare I say, arrogant assumption.