I've dismantled several fire-rings in an area that has many fire-rings strung out between a major trail and a river. (Colorado, 8,500 feet). These are not official camp sites.
Over the years, people decide to camp here rather than there even though a fire-ring was already there. Then they build a very large fire-ring, which is left brimming with ash, partially burned wood and unburnables such as aluminium foil and smashed cans. I'll dismantle one of these on my way out, tidy up the site, and carry out as much debris as I can.
Any hypothermic person can easily find another fire-ring. Most of these fire-rings are old, although still seen as an opportunity for a big campfire. I wouldn't dismantle an isolated fire-ring near timberline. Ethics?