Oh what have I started, the carby heat issue.
My employer has owned a fleet of 152s since the late 1970s and the aircraft have not suffered due to the carb heat being left on. The engine life may be reduced but they are replaced every 2000 hrs and as long as they last that long who cares. My employer is also a light aircraft maint organisation and they would let us know of any excessive FOD or ware.
When trying to teach landing we try to keep things as simple as possible, carb heat out downwind and in (using your thumb on right hand as you advance the throttle seems to work) on go-around or touch and go. If it is forgotten no big deal, the aircraft will climb at full flap with the carb heat on as long as the correct attitude is selected.
I DO understand that the way things are done are different but I don't think they are for the worse.