There may be legitimate concerns but the problem is that the government hasn't provided any actual proof, and doing this ban today opens up the possibility that there can be bans on American apps in future (and likely far more accepted since there's so much information already on Facebook and Microsoft's partnerships with spy agencies). Also, trying to keep people from using popular services is a difficult and costly exercise, there's every chance it becomes "cool" to get the app from a dark web source, much like prohibition couldn't stop alcohol