Under what legal rational can the U.S. government close my bitcoin business? They can't. Of course if you live under a tyrannical government then anything is possible. Singapore has a lot of crazy laws. Even chewing gum is illegal. But in the civilized world there is no way to do this. So let Singapore do what they will. It will only hurt them in the long run.
Kinda ironic given Vitalik resides in Singapore now. Hope he takes care & doesn't chew much gum.