Because a computer program is an expression, and the right to free expression is a cornerstone of the first amendment. So broadly, I don't think the government can "ban" an app, no matter who wrote it.

This proposition has been tested and affirmed for source code (see DeCSS t-shirt, etc.) but to my knowledge has not been tested for binaries. So, it would at minimum be a new test of whether binary code is as much a protected expression as human-readable code.