Putting all moral consideration aside, imagine you could totally depopulate two continents of your choosing. Why should any problem of modern economics be solved by that?
The concept of depopulation is simple enough to fit in a single sentence, it leaves out the real problem and its vast complexity (our linear economies and lifestyles attached to it), conveniently some one else is to blame and with all that, it is compatible to xenophobia. It ticks all boxes.
Of course, no problem would be fixed, the only thing you would buy with depopulation is time. The real problem is our unsustainable system, which is independent from any population count.
>We are too many people for what?
Is the question you fail to ask and answer. And going further this path of stupidly easy enemy stereotypes leads to all the societal atrocities you may have heard of.