1. A lot of archaeology is "rescue" archaeology. i.e. Either natural processes (e.g. rivers shifting) have threatened a site or the decision has been made to build, but there is a legal requirement to have the site surveyed and dug (if warranted). If you have an issue with this, then it must be with rivers shifting or people building. Rescue archaeology merely rescues the past from otherwise certain destruction.

2. Archaeologists are keenly aware that digging is a destructive act. There are countless examples of sites that were dug with unsophisticated techniques (e.g. bulldozers and dynamite) in the past that could have taught us far more were they dug with even slightly more modern (and careful) techniques. This is why, outside of rescue archaeology, excavations are done with careful deliberation. It's also standard practice to excavate sites only partially, leaving some of it intact for future archaeologists to dig with more advanced technology and techniques.

3. Rest assured, there yet remains vast quantities of history buried in the ground, waiting to be discovered. e.g. We have discovered cuneiform records referring to entire cities that remain buried and unknown. Other cities of the past are under modern settlements and are, at present, mostly inaccessible to archaeologists. It may seem like the world has been exhaustively explored, but there are still huge surprises waiting underground.