The basic theory is 100% correct. Increase the surface area facing the airflow as close to perpendicular as possible, increases the drag and will slow you down if all other factors remain equal.
Has nothing to do with bad airmanship or bad habits IMHO, simply whether your airplane can deal with it or not. The turboprop I flew before (geared turbine, not free) did not really care and the manuals listed it as a method of deceleration available if needed. No adverse effects listed. Used very situational, sometimes to allow us to keep high speed down to 4-5 miles to skip ahead in the sequence if the controller could fit us in. Lots of fun, 250kts until 5nm and stabilized by 3nm. Props full forward helped a great deal.
Would not try it on others planes without doing my homework first, but that should be standard anyway.