Only if we assume that our mitigation efforts against those other problems would be lacking for resources, if we sent some resources to work on space object det

Only if we assume that our mitigation efforts against those other problems would be lacking for resources, if we sent some resources to work on space object detection/defense. If we're putting as much money and effort into automobile safety as society wants/will allow, there's no 'loss' in taking additional funds to tackle the next problem down the line. And so on.