This loan thing is depending what is the situation. It's dumb to say that investing loaned money is absolutely wrong or that it's right. Many people spend rest of their lives in debt hell and investing some of that to bitcoin might be the way to get rid of that debt. There's risk but you have to calculate those risks based on your situation.
When you're in a hole, dig faster?
Maybe you can do a 180 curve while digging and get out of that hole.
This is why so many poor people buy lottery tickets...
Yeah, but there's smaller risks in bitcoin than in lottery. All decision in life have risks, important thing is to try to learn them. Good way of not learning these risks is to obey some principle like "don't ever invest loaned money" and not thinking why?