Banks originated as goldsmiths who stored people's gold and gave out paper certificates representing the quantity of gold that was stored. This was a valuable service, because storing gold was hard, and paying people with gold was hard. Bitcoins are very different. Storing them is in principle easy, especially if you have a bitcoin-only device as I advocated
here, and paying people with them is easy. All of the reasons for putting your gold in the bank are thus irrelevant for bitcoins.
Some of them are, some of them aren't. If you don't store your currency in a bank, the opportunity value of the held currency is forever lost.
Will you give me 100 bitcoins today if I promise to give you 100 bitcoins next year? Of course not -- even if you 100% trust me, you're still giving up the opportunity value of being able to spend those bitcoins within the next year should you choose to do so. There's no reason you should give that up in exchange for nothing. If you hold your bitcoins, that's exactly what you're doing.
I don't understand what you're saying. Your argument seems to imply the exact opposite of your conclusion. You seem to be saying that if you want to be able to use your money at any time, you should let someone else take care of it. But actually, when you do that, you are risking losing access to your money, because they may run off with it, or do something else irresponsible with it and lose it. And you also seem to argue that this is why you shouldn't hold on to your money... because then you can't use it when you want. But exactly the opposite of this is true. It is only when you have it that you can use it when you want.
The opportunity value is decreased, not increased, by storing money in a bank.