Are people only trading the crypto they borrow or withdrawing and doing other things with it (possibly in the real world?)
If people are mainly just trading what they borrow, what happens if they lose all of it/a lot of it and can pay back the amount?
I haven't looked into defi before now (and your English is a little stilted), but if I'm reading your question correctly, then I can see a big crash coming in the defisphere. Borrowing and not paying back in this forum is seen as a scam. Once people get a taste for borrow/not pay back/borrow again, we'll see a whole new wave of scams occurring.
Think Mortgage Subprime. Debt was on-sold to those who thought they could make a quick buck, then on-sold again (and again). The debt never went away.