So I took it once more to look at shorting in Bitshares today.
I must say I'm slightly confused

Let's take NZD as an example.
Feed price: 138.082 BTS/bitNZD
Margin Call Price: 151.8902 BTS/bitNZD
Ok. So, from the beginning, we have to lock up some BTS as collateral (>= 1.95x) in case the BTS loses value against NZD.
The higher the collateral ratio, the higher the margin call price.
So far so good.
I then tried to sell my newly minted smartcoins to another account of mine, naively thinking that would settle the original debt (by getting rid of the smartcoins, I wondered if some automatic action would be taken).
It didn't -
which, if I understand correctly, means that someone, somewhere, must be perpetually in debt in order for any smartcoin to be in circulation?Fine, I then tried to close the position: no luck, I needed the 10 smartcoins I'd just sold to the other account.
Transferred them back, clicked "Close position", the smartcoins disappeared, I got all of my BTS back.
The total supply of CHF and NZD (where I ran the tests) shrinked back to what it was originally.
So even if I wanted to offer some limited liquidity, that would always mean making a bet that BTS would appreciate against the smartcoin, perpetually.
And here's the mind-boggling part: let's say I shorted 1000 NZD into existence, and by the grace of .. doge, BTS did move favorably against NZD.
I now have (let's say) 200 NZD in my pocket! Wow! So I close position and that's that, I have 200 NZD in my wallet, debt-free.
.... why not simply hold the BTS, avoid locking up 1.95x the amount, go into debt, and change the BTS for BTC or something less volatile ?
ELI5 please.