Just wanted to write something about the word "IOU" that seems to be a symbol for what's good or bad in LN 
IOUs in the Bitcoin world have a bad reputation basically because of exchange defaults like MtGox's insolvency. Of course, you can call a HTLC an "IOU". But the type of IOU exchanges offer to you are extremely different from these offered by LN.
The difference is actually in the way disputes are resolved. A conflict with a centralized exchange about an IOU can only be solved with human intervention, in severe cases the the judiciary system must be involved and the conflict may not be solved at all. In LN, however, you have a totally automated, not compromittable (if not destinating very large funds to double spend via 51% attack) and very predictable dispute solving instance - the Bitcoin blockchain.
Imagine an exchange offering you the same type of security for their IOUs. I, for myself, would use them
LN Bitcoins ("msats") are not equal to blockchain-Bitcoins, but they are backed by Blockchain BTC in a much more reliable way than all centralized wallet providers, exchanges, etc. can provide. And most (if not all) Bitcoin users still use these centralized providers, so why shouldn't they use LN if it's even better?
IOUs in the Bitcoin world have a bad reputation basically because of exchange defaults like MtGox's insolvency. Of course, you can call a HTLC an "IOU". But the type of IOU exchanges offer to you are extremely different from these offered by LN.
The difference is actually in the way disputes are resolved. A conflict with a centralized exchange about an IOU can only be solved with human intervention, in severe cases the the judiciary system must be involved and the conflict may not be solved at all. In LN, however, you have a totally automated, not compromittable (if not destinating very large funds to double spend via 51% attack) and very predictable dispute solving instance - the Bitcoin blockchain.
Imagine an exchange offering you the same type of security for their IOUs. I, for myself, would use them
LN Bitcoins ("msats") are not equal to blockchain-Bitcoins, but they are backed by Blockchain BTC in a much more reliable way than all centralized wallet providers, exchanges, etc. can provide. And most (if not all) Bitcoin users still use these centralized providers, so why shouldn't they use LN if it's even better?