ITU seems to have control over a large portion of the hardware that allows for people to connect to the internet. As this power is amassed by a single entity (no matter how benign that entity may be), then there are vulnerabilities. It is not hard for corruption to infiltrate even the most well-meaning organizations. It is best to keep power diffuse.
One month ago I would have said no. That was before Syria's internet blackout. That made me realize in fact how it is not only logistically possible, but not that difficult for a government to achieve. The fact that the ITU is a UN group and not a US group is what poses a threat. The US will never directly interfere with an open internet. The US, however, may not have a choice if it is voted upon at the UN. Even though they could simply say they would not participate, violating UN law hurts a nation in many ways, most of which not related to the agreement violated.
ITU is not a threat to the internet. At least not yet. There are much bigger things out there that are considered threats. ITU has not made a big influence on the internet and since we have been aware of them, nothing has really changed. This could switch up in the future, but as of right now ITU is not a threat.
The ITU has been around for a while. To say that suddenly free open internet will be changing is hasty at best. Down the road changes will happen, but the internet is something that many people will rise up and fight for to keep the way it is. Bills have tried to pass recently implementing censored or even traced internet usage. All of this will fall, but it won't be down forever.