I think facebook is the worst threat of libra
Yes, it is, and I don't think facebook have a good reputation to keep your money, it's dangerous, they already have all our data and they use this in a non ethical way, and now they want to take care our money?
So I really think facebook is the worst think for libra
If they create an application (or integrate it into their own, e.g. facebook) they will be able to replace the people's internet bank application with their own.
In this case people will do their banking thru their facebook page and facebook could make money on that too. Most of the average joes trust facebook and usually these people don't really care about the security of their money (usually because they have debt instead of money but I'm just generalizing...)
So if they take over the banking, they (facebook) will be able to offer some financial related stuff to the people and can make money on this too, not only on ads. And in this case there's no need for new coin... (in case EU and others won't let them use their coin or with heavy restrictions...)