That would be playing dice with the survival of the human species. Many scientific bodies oppose research into the NEO threat on the grounds that such programmes might divert funding from their particular fields. While this is perfectly understandable from a narrow perspective, it is an abrogation of the responsibility of science to safeguard humankind, or at least to alert it to threats to its well being. Planetary Defence is a multi-disciplinary undertaking. Astronomers have been at the forefront of the search for, and detection of NEOs, but planetary scientists, geologists, palaeontologists, biologists, physicists and many others have been deeply involved in piecing together the jigsaw that has resulted in our current state of knowledge.
Scientists are concerned with the acquisition and interpretation of new data.
A planetary defence programme would have to do so. The funding and resources required to detect and track all NEOs cannot therefore be justified on scientific research grounds. Defence is usually the prerogative of the military, but there is some resistance from the defence establishment to becoming involved in planetary defence. The normal reasons for inaction invoke the inability of a single nation to achieve very much, though this ignores the essentially international nature of planetary defence. The weak excuses hide the real reason - money.