Affiliate Marketing Secrets

I’m trying to get some information about creating a social network with buddypress. I’m not talking about creating another Facebook but my site would be more like a linkedin website for a niche community. So I would have features such as profiles, messages, employer page and employees page, contacts, chat. Is buddypress good platform for a website like that?

“When Facebook launched, social networking was not mainstream. Now, with popular competition like Twitter, Google+ and LinkedIn, along with dozens of niche networks and MySpace lurking on the horizon, users have other choices. If Facebook was free forever, the resulting concerns about data and privacy begs the questions – would users really stay?”
I’m from Japan.
I don’t understand what the last sentence in the text above means, among others,
“beg the questions” and ” would user really stay?”.
Could anyone kindly paraphrase or clarify them?
I’ll appreciate your help.