As a parent now myself, I've used the "because I said so" line.
I have a personal rule however. When I've used it, I make a point to sit down and explain why. It might be after we have all cooled off, or after the stress is gone.
It gives them a sense of what went wrong. In the moment, they also know they will get an explanation eventually. Lastly, it keeps me honest. No using it because I can't explain in a way that doesn't make me look bad.
It's worth noting, parenting is HARD. Our generation at least has the advantage of modern information and science. The generations before us were stuck with hearsay and hope. Recognise their mistakes, but try not too judge them too harshly for them.