Email is a protocol. Phones are a protocol. Facebook is... a company. I don't like the idea that the coming nexus of communication is a single-company provider, with zero incentive to open up a "facebook message protocol"... they simply want to be the only source of communication.
Yes, but I can switch companies when I'm not happy with my current company or don't like their policies. Also, my AT&T phone can call my friend's Verizon phone.
You find it scary that they want that, or that this is how it is turning out? I don't think the former is scary -- that's obviously their best bet for paying their bills. There's nothing scary about Facebook not wanting to reduce their ad impressions by allowing me to talk to my friends on FB via Outlook.
If the latter is actually what worries you, then there's nothing we can really do about that, nor should FB be forced into changing the way things are working out for them. There is a lot of value in a central hub. Email sucks for what FB is great for and decentralized hubs for FB-like communication will likely always suck unless there is great cooperation between disparate hubs and a great way to ensure there is a level of trust between data sources. Not likely to be developed in the near future. It's a difficult problem, but there may be some hope with the Semantic Web initiative and with linked data. Either way, you will most likely be signed up with one of those hubs and that will be your hub.
I'm not suggesting they should be forced into anything, and I don't have a problem with the idea of a person using a central hub; I use google applications for tons of things, for documents, calendar, etc. What I don't like is that to communicate with anyone using the facebook hub, you have to also be using it. I can use nothing but gmail for my communications, but someone using hotmail can easily communicate with me.
An equally serious problem is that Facebook makes no assurances whatsoever about whether they will choose to filter/censor communication (as they did here http://techcrunch.com/2010/11/22/facebook-censorship/). If I/a business want to be absolutely sure that any mail sent to me will get to me and never be deleted or censored, I can buy a domain and run my own email hosting; it's not a the whim of some external company.
I find this scary.