When bitcoin is open-source, what stops people from making more bitcoin-like coins?
Discussion
Nothing. In fact, they've done it multiple times.
But you can't call them bitcoin?
Nothing. But they’ll never catch up to the adoption BTC has achieved. It’s too late. That ship has sailed.
You can achieve the initial valuation from 0 to non-0 only once. Every new attempt will start at a non zero value, and therefore it will be a flawed launch.