Why? By using Coinbase you are saying, "I don't want to hold any bitcoins myself, I want a bank to hold some value, denominated in BTC, on my behalf". For all depositers care, Coinbase might have zero Bitcoins issued before the fork.
It's like depositing a dollar to a bank, and then finding out that it had been signed by Andy Warhol in invisible ink and asking for the specific dollar back. Sorry, you shouldn't have deposited in a bank. You can get a dollar back, but not the same one you deposited.
What you're looking for is more like a safety deposit box for Bitcoins. That's a whole separate product, with a different fee structure.
Let's say there is a court case where the judge awards all shareholders of AAPL $100 of compensation for every share held (It's to the shareholders, but not the company, because the court case involved shareholders vs management). The government sends $100 per share to each registered holder. Your investment fund is the registered holder of AAPL securities instead of you. Do you get $100 per share that was held on your behalf, or do the operators of the investment fund get it?
Isn't that just a dividend at that point? In the real world investment funds have fairly complex dividend rules (how much is reinvested in the fund, how much is skimmed for fund manager fees, etc), and regulations have managed to force such funds to disclose all of those policies up front (prospectus) and keep them up-to-date.
In the other fork in this discussion thread, the banking analogy: we're talking about an exotic interest payment of sorts. Again here, banking regulations require banks to disclose interest rates and payment details and management fees up front for accounts. But banks in the real world are largely allowed to reap the majority of profits from an investment that goes well, and doesn't have to apply much if any of that back to the savings accounts from which it utilized stored funds to fund that investment.
Which is to say that Coinbase may be doing nothing wrong according to either real world analogy, with the big difference being the "wild frontier" of existing in an under-regulated space with fewer up-front disclosure guarantees.
Both this and dividends are payments to shareholders but this is different because it's not funded by the company itself. It's a third party electing to pay every shareholder. Also, dividends are regular events, but getting a new asset that can be traded is not.
I guess that depends too on what you think "the company" is in this case, going back to struggling with whether or not this analogizes to a stock split or not.
I think that's a great analogy for each of us thinking about our own ethical intuition. But if you're literally asking what would actually happen, I'm guessing the answer is...there would probably be a lawsuit and the courts would figure it out. Which is probably exactly what will happen here, if Coinbase continues to not support the Bitcoin fork and its value holds long enough.
The only argument you can make is Coinbase not givint a "reasonable" amount of foresight to users (who would pressumble have the right of advanced time/knowledge to convert to USD, etc and then back to BTC (on another "exchange").
I have no idea is this is true or not, but this is the only criticism of Coinbase you can have here.
It's like depositing a dollar to a bank, and then finding out that it had been signed by Andy Warhol in invisible ink and asking for the specific dollar back. Sorry, you shouldn't have deposited in a bank. You can get a dollar back, but not the same one you deposited.
What you're looking for is more like a safety deposit box for Bitcoins. That's a whole separate product, with a different fee structure.