Only if you're averaging with the trend in your time frame. If the trend line in your investment time frame breaks down, you should scale out of the position IMHO.
IMO only if you are doing contrarian investing with a given risk profile where a lower price means a better bargain.
Amazing how you could come to such a conclusion. If you were to take a poll of long-time investors who manage a significant amount of money (especially their own)..... it's likely the result would be more like, "it's NEVER acceptable to average down"...
I really think the time frame is the important thing. Investors who started and added to positions during the crash and secondary dip to March lows may have been averaging down based on stocks being fundamentally on sale at bargain prices, knowing that in their 5- to 20-year investing time frame they would make a killing.
Oh, then let me amend the premise... "It's NEVER acceptable to average down... unless you're 100% SURE your stock is going to bounce back really, REALLY big (you know, so that you can make a killing)..."