Forest management is a diverse field, and thinning a forest for fuel reduction is a well-recognized practice. If done right, of course -- large-scale clear-cutting and management to maximize cut are not thinning.

Many private and conservancy-type forest management groups do thinning, and controlled burning to manage understory and reduce the chances for a forest-destroying crown fire. There's pretty good evidence that Native Americans did it too, though possibly for other reasons such as improving the range for hunting purposes. That in fact has not been a major part of the Forest Service's practice, because it requires trained staff and costs money. Neither of which they have been granted for that purpose, so it's not a priority. Some private forests, too, are managed by selective cutting (Pacific Lumber Company used to do that, before the hedge fund takeover) for sustainable harvest. The National Parks have also done thinning and controlled burns in a number of places (including Yosemite Valley) - smoke in the valley from such fires has been a problem in the past, but not to the extent seen now.