This is a real cause and I say BS right back to you bubba, if you wanna run used motor oil in your saws. Becasue doing that will cause a lot of harm to you and your saw, as well as to people and critters around you. Heavy metals and blowby are highly toxic. Per your request here, if I can convince only ONE of the readers here on this forum to avoid using used motor oil in a saw to lube the bar, I am doing them and the world around them a lot of good.
I would say the same thing about using TWC marine premix in your saws, which I have argued with other people about on this forum. TWC rated premix oil is not designed to run in air cooled chainsaw engines, and you will be far better served to run JASO FB/FC/FD rated oil, preferebly FC or FD. I would go further to say that you are better off not running chainsaws with high vibration for long periods of time as well, or you are far more likly to develop problems like tendonitis, white finger, and arthritis. For that reason I would avoid running a Stihl 880 and 180 chainsaw, as they all have excessively high vibration ratings which commonly lead to medical problems. However, these two issues only inflict damage on your saw and yourself, so in my view they are far lesser issues than using used bar oil in a saw, which does greater damage than to just you and your saw.
One thing they teach us in avalanche rescue training every year (I am a member of the ski patrol). Humans have the inate problem of following other humans no matter what the risk. For that reason I have to go on search and rescue missions every winter here, and it is the same story over and over again. One person saw another person going out of bounds into a restricted area, and hey, they were fine, so I will be fine.. and whoooomph. Down the mountain they go. If they are buried, they are usually dead within 15 minutes. Then we have to find them and dig them out. While this is dramatic and unrelated to chainsaws, it still illustartes my point; just becasue some people do things and do not think it is a big deal, it does not mean that it is a good thing to do. You have to determine if the risk is worth the reward, and you have to realize that doing some things may well have a lot higher risk than they appear to have. Just becasue some bozo does something and says it is a good thing to do, does not mean it is a good thing to do.