If martingale worked there would be a lot of dead dice sites but sadly I have tried to use it and end up losing all.
That is actually a good argument. People are still believing in martingale, so you could use that to convince them
People believe in it because in theory, it would work. The reality, though, is that there are two things stopping it:
1) Player bankroll
2) Site max bet allowance
One of these is going to be hit, as neither of these can be infinite. Should these be removed, it would change things, as you could lose millions of times in a row and still not have "lost" yet.
Even in theory there is a third limitation: House could just stop anytime they want to. So if you are down 40 bets in a row, they could just say: "Thanks, good bye"
This is true as well, but we make decisions based on the assumption this won't happen. Otherwise we wouldn't be playing on the site/in that casino regardless as to if we wanted to martingale or not,
.But it is a good point, that there's also the risk of them running. And in that case, when dealing with cryptos we can throw out another: the risk that the site is hacked (or "hacked") while you're trying to martingale.
That is the problem, there are so many limitations that even theoretical its impossible. But its a nice thought experiment nontheless. People have been grinding their brain on this for centuries for a reason.