> If you win money at a casino and deposit it at a bank, the bank doesn't know where you got the cash from.
You're off base here. There's serial numbers on money and many databases maintained both public and private meant to track those and flag inflows of marked bills. The bank absolutely might know where you got the cash from -- the difference is that there are legal guarantees for the fungibility of cash. It is enforced by law that if someone pays you a dollar, you are legally obligated to accept that as tender. For all debts both public and private.
The fungibility of the dollar is not rooted in lack of ability to track dollars, it is rooted in state violence.
Anyways everyone should use Monero. BTC is obviously far less fungible than a dollar.
You're right about dollars being only legally-fungible. It's been hypothesized that there are databases tracking when and where dollars are used based on serial numbers, but to my knowledge, there hasn't been any reliable confirmation of that. If there is such a database, at least it's not publically available like Bitcoin's is. So, I agree with you that Monero should be used over Bitcoin (disclaimer, I own some XMR).
BTC has a history, so if I had 1 BTC, and you had 1 BTC, they wouldn't be equivalent.
When you deposit BTC into a Coinbase account from a gambling site, CB shuts down your account. That is irrefutable proof that BTC is not fungible.
Compare it to cash which is fungible. If you win money at a casino and deposit it at a bank, the bank doesn't know where you got the cash from.