Thanks for the grace there, and that's a problem we are solving. You might have X contacts on Circles but you're only going to see from those you have placed in a circle. So only content from people you actually want to see from.
In terms of syncing contacts, we don't store any contact book information on our servers. We pass through the contact book to see if a user exists there, we return them back as a connection. If not we return them as someone you can invite.
But... Again, you expect me to trust you. And if I don't trust Facebook or other well-known contacts to use my contacts appropriately, why would I trust what appears to be two random individuals in the UK to not retain that information? Are we supposed to forget the lessons of the past with all of the apps that have used our data inappropriately?
Do you log who someone has looked up in Circles when they join? If you do then you could trivially reconstruct someone's contact book.
That's what Facebook were found to be doing, except they were actually creating 'shadow profiles' for the contacts.
But let's assume for the moment that you aren't running a contact harvesting scam... I hardly use Facebook and I'm very particular about who I add on there. I actually go back and remove people I don't interact with or who create noise --I want to be able to log in once a week and see what people are doing, not scroll through memes or other crappy shared content.
My contact list on my phone, on the other hand, has friends, ex-friends, family, current and former coworkers, etc. Most of them I don't want to be connected with on a social network.
So I guess what I'm saying is that from my perspective, you aren't solving any problems, and are just a potential security risk when it comes to sucking up contact information.