...taking on all refugees is more complicated than regular immigration when e.g. the host country would typically pick and choose by setting requirements for age, education, etc. ....
Anyone with half a brain would exclude certain medical conditions, such as tuberculosis positive. And criminals of various sorts. "Open borders" seems to have started about two decades ago with a Soros funded think tank. It's related to diminishing power of individual states and strengthening "world government."
There is a theory in economics that one way a government can give away more than it can actually afford to, is to have continued population growth. Then the next generation can pay the overly generous pensions, health care and such to the last.