But in your case, you may not only loose your btc(you will have them less when time come) but even dont have enough btc to payback. That`s the tricky place.
Again, lend me 100 BTC now, deposit it... call it as you want... I promise to pay you back 110 BTC in one year from now...
For other side, MMM\Casino say clearly that you might not get your money back, but the interest is so high that people might not even care.
I will lock 110 BTC in escrow for you.
In that case people would love to do so,but i still would like to remind you that escrow is not 100% safe, especially in a long terms, because person can get missing,pc corrupt, etc.
We live in real life, there is no 100% sure.
In case of one sort terms\high rates this is acceptable, but in long term you`ll have to use some certified organization, which is none, all btc storages get btc stolen in a while)