I am unclear as to how one can propose to be a humanitarian and also advocate the extinction of the human race. At first glance, this does seem to be a contradiction. We may already be entering the die off stage, with 40,000 children dying each day from preventable causes. If the parents of these children had the freedom to choose not to conceive, most of them wouldn't have been sentenced to a short, tragic life and painful death.
Reproductive freedom is a major first step toward voluntary human extinction.
My perspective is more Earth-centered, so the answer to this question is obvious to me. However, even with a human-centered perspective, we should care about other life because, whether we realize it or not, we are dependent on them for our survival. By reducing biodiversity as we are doing, we are sawing off the limb we stand on. If you truly care about helping to end suffering, then do something useful. Of course you must be well aware of the countless ways that exist to alleviate suffering within the world and more specifically within your community.